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In [[number theory]], an '''aurifeuillean factorization''', named after [[Léon-François-Antoine Aurifeuille]], is a special type of [[algebra]]ic [[factorization]] that comes from non-trivial factorizations of [[cyclotomic polynomial]]s over the [[integer]]s.<ref>{{cite journal |url=https://www.ams.org/journals/mcom/2006-75-253/S0025-5718-05-01766-7/S0025-5718-05-01766-7.pdf |title=Aurifeuillian factorization |author=A. Granville, P. Pleasants |journal=Math. Comp. |volume=75 |issue=253 |year=2006 |pages=497–508 |doi=10.1090/S0025-5718-05-01766-7|doi-access=free }}</ref> Although cyclotomic polynomials themselves are [[irreducible polynomial|irreducible]] over the integers, when restricted to particular integer values they may have an algebraic factorization, as in the examples below.
In [[number theory]], an '''aurifeuillean factorization''', named after [[Léon-François-Antoine Aurifeuille]], is [[factorization]] of certain integer values of the [[cyclotomic polynomial]]s.<ref>{{cite journal |url=https://www.ams.org/journals/mcom/2006-75-253/S0025-5718-05-01766-7/S0025-5718-05-01766-7.pdf |title={{not a typo|Aurifeuillian}} factorization |author=A. Granville, P. Pleasants |journal=Math. Comp. |volume=75 |issue=253 |year=2006 |pages=497–508 |doi=10.1090/S0025-5718-05-01766-7|doi-access=free }}</ref> Because cyclotomic polynomials are [[irreducible polynomial]]s over the integers, such a factorization cannot come from an algebraic factorization of the polynomial. Nevertheless, certain families of integers coming from cyclotomic polynomials have factorizations given by formulas applying to the whole family, as in the examples below.


== Examples ==
== Examples ==
* Numbers of the form <math>a^4 + 4b^4</math> have the following factorization ([[Sophie Germain's identity]]): <math display=block>a^4 + 4b^4 = (a^2 - 2ab + 2b^2)\cdot (a^2 + 2ab + 2b^2).</math> Setting <math>a=1</math> and <math>b=2^k</math>, one obtains the following aurifeuillean factorization of <math>\Phi_4(2^{2k+1})=2^{4k+2}+1</math>, where <math>\Phi_4(x)=x^2+1</math> is the fourth cyclotomic polynomial:<ref name="Wolfram">{{MathWorld|title=Aurifeuillean Factorization|urlname=AurifeuilleanFactorization}}</ref> <math display=block>2^{4k+2}+1 = (2^{2k+1}-2^{k+1}+1)\cdot (2^{2k+1}+2^{k+1}+1).</math>

* Numbers of the form <math>a^6 + 27b^6</math> have the following factorization, where the first factor (<math>a^2 + 3b^2</math>) is the algebraic factorization of [[sum of two cubes]]: <math display=block>a^6 + 27b^6 = (a^2 + 3b^2)\cdot (a^2 - 3ab + 3b^2)\cdot (a^2 + 3ab + 3b^2).</math> Setting <math>a=1</math> and <math>b=3^k</math>, one obtains the following factorization of <math>3^{6k+3}+1</math>:<ref name="Wolfram"></ref> <math display=block>3^{6k+3}+1 = (3^{2k+1}+1)\cdot (3^{2k+1}-3^{k+1}+1)\cdot (3^{2k+1}+3^{k+1}+1).</math> Here, the first of the three terms in the factorization is <math>\Phi_2(3^{2k+1})</math> and the remaining two terms provide an aurifeuillean factorization of <math>\Phi_6(3^{2k+1})</math>, where <math>\Phi_6(x)=x^2-x+1</math>.
* Numbers of the form <math>a^4 + 4b^4</math> have the following aurifeuillean factorization (see also [[Sophie Germain#Honors_in_number_theory|Sophie Germain's identity]]):
* Numbers of the form <math>b^n - 1</math> or their factors <math>\Phi_n(b)</math>, where <math>b = s^2 \cdot t</math> with [[square-free integer|square-free]] <math>t</math>, have aurifeuillean factorization if and only if one of the following conditions holds:
:: <math>a^4 + 4b^4 = (a^2 - 2ab + 2b^2)\cdot (a^2 + 2ab + 2b^2)</math>

* Setting <math>a=1</math> and <math>b=2^k</math>, one obtains the following aurifeuillean factorization of <math>2^{4k+2}+1</math>:<ref name="Wolfram">{{MathWorld|title=Aurifeuillean Factorization|urlname=AurifeuilleanFactorization}}</ref>
:: <math>2^{4k+2}+1 = (2^{2k+1}-2^{k+1}+1)\cdot (2^{2k+1}+2^{k+1}+1)</math>

* Numbers of the form <math>a^6 + 27b^6</math> have the following aurifeuillean factorization (the first factor (<math>a^2 + 3b^2</math>) is the algebraic factorization of [[sum of two cubes]]):
:: <math>a^6 + 27b^6 = (a^2 + 3b^2)\cdot (a^2 - 3ab + 3b^2)\cdot (a^2 + 3ab + 3b^2)</math>

* Setting <math>a=1</math> and <math>b=3^k</math>, one obtains the following aurifeuillean factorization of <math>3^{6k+3}+1</math>:<ref name="Wolfram"></ref>

:: <math>3^{6k+3}+1 = (3^{2k+1}+1)\cdot (3^{2k+1}-3^{k+1}+1)\cdot (3^{2k+1}+3^{k+1}+1)</math>

* Numbers of the form <math>b^n - 1</math> or <math>\Phi_n(b)</math>, where <math>b = s^2 \cdot t</math> with [[square-free integer|square-free]] <math>t</math>, have aurifeuillean factorization if and only if one of the following conditions holds:
** <math>t\equiv 1 \pmod 4</math> and <math>n\equiv t \pmod{2t}</math>
** <math>t\equiv 1 \pmod 4</math> and <math>n\equiv t \pmod{2t}</math>
** <math>t\equiv 2, 3 \pmod 4</math> and <math>n\equiv 2t \pmod{4t}</math>
** <math>t\equiv 2, 3 \pmod 4</math> and <math>n\equiv 2t \pmod{4t}</math>
: Thus, when <math>b = s^2\cdot t</math> with square-free <math>t</math>, and <math>n</math> is [[modular arithmetic|congruent]] to <math>t</math> modulo <math>2t</math>, then if <math>t</math> is congruent to 1 mod 4, <math>b^n-1</math> have aurifeuillean factorization, otherwise, <math>b^n+1</math> have aurifeuillean factorization.
: Thus, when <math>b = s^2\cdot t</math> with square-free <math>t</math>, and <math>n</math> is [[modular arithmetic|congruent]] to <math>t</math> modulo <math>2t</math>, then if <math>t</math> is congruent to 1 mod 4, <math>b^n-1</math> have aurifeuillean factorization, otherwise, <math>b^n+1</math> have aurifeuillean factorization.


* When the number is of a particular form (the exact expression varies with the base), Aurifeuillian factorization may be used, which gives a product of two or three numbers. The following equations give Aurifeuillian factors for the [[Cunningham project]] bases as a product of ''F'', ''L'' and ''M'':<ref>{{cite web|title=Main Cunningham Tables|url=https://homes.cerias.purdue.edu/~ssw/cun/pmain423.txt}} At the end of tables 2LM, 3+, 5-, 6+, 7+, 10+, 11+ and 12+ are formulae detailing the Aurifeuillian factorisations.</ref>
* When the number is of a particular form (the exact expression varies with the base), aurifeuillean factorization may be used, which gives a product of two or three numbers. The following equations give aurifeuillean factors for the [[Cunningham project]] bases as a product of ''F'', ''L'' and ''M'':<ref>{{cite web|title=Main Cunningham Tables|url=https://homes.cerias.purdue.edu/~ssw/cun/pmain524.txt}} At the end of tables 2LM, 3+, 5-, 6+, 7+, 10+, 11+ and 12+ are formulae detailing the aurifeuillean factorizations.</ref>


: If we let ''L'' = ''C'' − ''D'', ''M'' = ''C'' + ''D'', the Aurifeuillian factorizations for ''b''<sup>''n''</sup> ± 1 of the form ''F'' * (''C'' − ''D'') * (''C'' + ''D'') = ''F'' * ''L'' * ''M'' with the bases 2 ≤ ''b'' ≤ 24 ([[perfect power]]s excluded, since a power of ''b''<sup>''n''</sup> is also a power of ''b'') are:
: If we let ''L'' = ''C'' − ''D'', ''M'' = ''C'' + ''D'', the aurifeuillean factorizations for ''b''<sup>''n''</sup> ± 1 of the form ''F'' * (''C'' − ''D'') * (''C'' + ''D'') = ''F'' * ''L'' * ''M'' with the bases 2 ≤ ''b'' ≤ 24 ([[perfect power]]s excluded, since a power of ''b''<sup>''n''</sup> is also a power of ''b'') are:


: (for the [[coefficient]]s of the [[polynomial]]s for all square-free bases up to 199 and up to 998, see <ref>[https://stdkmd.net/nrr/repunit/repunitnote.htm#aurifeuillean List of Aurifeuillean factorization of cyclotomic numbers (square-free bases up to 199)]</ref><ref>[http://myfactorcollection.mooo.com:8090/LCD_2_199 Coefficients of Lucas C,D polynomials for all square-free bases up to 199]</ref><ref>[http://myfactorcollection.mooo.com:8090/LCD_2_998 Coefficients of Lucas C,D polynomials for all square-free bases up to 998]</ref>)
: (for the [[coefficient]]s of the [[polynomial]]s for all square-free bases up to 199 and up to 998, see <ref>[https://stdkmd.net/nrr/repunit/repunitnote.htm#aurifeuillean List of aurifeuillean factorization of cyclotomic numbers (square-free bases up to 199)]</ref><ref>[http://myfactorcollection.mooo.com:8090/LCD_2_199 Coefficients of Lucas C,D polynomials for all square-free bases up to 199]</ref><ref>[http://myfactorcollection.mooo.com:8090/LCD_2_998 Coefficients of Lucas C,D polynomials for all square-free bases up to 998]</ref>)


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== History ==
== History ==
In 1869, before the discovery of Aurifeuillean factorizations, {{ill|Fortuné Landry|lt=Landry|fr||es||de}}, through a tremendous manual effort,<ref name="numericana">[http://www.numericana.com/answer/numbers.htm#aurifeuille Integer Arithmetic, Number Theory – Aurifeuillian Factorizations], Numericana</ref><ref name="primepages">[https://primes.utm.edu/glossary/page.php?sort=GaussianMersenne Gaussian Mersenne], the [[Prime Pages]] glossary</ref> obtained the following factorization into [[prime number|primes]]:
In 1869, before the discovery of aurifeuillean factorizations, {{ill|Fortuné Landry|lt=Landry|fr||es||de}}, through a tremendous manual effort,<ref name="numericana">[http://www.numericana.com/answer/numbers.htm#aurifeuille Integer Arithmetic, Number Theory – Aurifeuillean Factorizations], Numericana</ref><ref name="primepages">[https://primes.utm.edu/glossary/page.php?sort=GaussianMersenne Gaussian Mersenne], the [[Prime Pages]] glossary</ref> obtained the following factorization into [[prime number|primes]]:


:<math>2^{58}+1 = 5 \cdot 107367629 \cdot 536903681.</math>
:<math>2^{58}+1 = 5 \cdot 107367629 \cdot 536903681.</math>
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== External links ==
== External links ==
* [http://pagesperso-orange.fr/colin.barker/lpa/cycl_fac.htm Aurifeuillian Factorisation], Colin Barker
* [http://pagesperso-orange.fr/colin.barker/lpa/cycl_fac.htm Aurifeuillean Factorisation], Colin Barker
* [http://www.numericana.com/answer/numbers.htm#aurifeuille Aurifeuillian Factorizations], Gérard P. Michon
* [http://www.numericana.com/answer/numbers.htm#aurifeuille Aurifeuillean Factorizations], Gérard P. Michon
* [https://homes.cerias.purdue.edu/~ssw/cun/mine.pdf The Search for Aurifeuillian-Like Factorizations]
* [https://homes.cerias.purdue.edu/~ssw/cun/mine.pdf The Search for Aurifeuillean-Like Factorizations]
* [http://myfactors.mooo.com/ Online factor collection]
* [http://myfactors.mooo.com/ Online factor collection]
* [https://www.unshlump.com/hcn/aurif.html A Note on Aurifeuillian Factorizations]
* [https://www.unshlump.com/hcn/aurif.html A Note on Aurifeuillean Factorizations]
* [http://pagesperso-orange.fr/colin.barker/lpa/cycl_fac.htm Aurifeuillian Factorisation]
* [http://pagesperso-orange.fr/colin.barker/lpa/cycl_fac.htm Aurifeuillean Factorisation]


[[Category:Number theory]]
[[Category:Number theory]]

Latest revision as of 19:41, 29 May 2024

In number theory, an aurifeuillean factorization, named after Léon-François-Antoine Aurifeuille, is factorization of certain integer values of the cyclotomic polynomials.[1] Because cyclotomic polynomials are irreducible polynomials over the integers, such a factorization cannot come from an algebraic factorization of the polynomial. Nevertheless, certain families of integers coming from cyclotomic polynomials have factorizations given by formulas applying to the whole family, as in the examples below.

Examples

[edit]
  • Numbers of the form have the following factorization (Sophie Germain's identity): Setting and , one obtains the following aurifeuillean factorization of , where is the fourth cyclotomic polynomial:[2]
  • Numbers of the form have the following factorization, where the first factor () is the algebraic factorization of sum of two cubes: Setting and , one obtains the following factorization of :[2] Here, the first of the three terms in the factorization is and the remaining two terms provide an aurifeuillean factorization of , where .
  • Numbers of the form or their factors , where with square-free , have aurifeuillean factorization if and only if one of the following conditions holds:
    • and
    • and
Thus, when with square-free , and is congruent to modulo , then if is congruent to 1 mod 4, have aurifeuillean factorization, otherwise, have aurifeuillean factorization.
  • When the number is of a particular form (the exact expression varies with the base), aurifeuillean factorization may be used, which gives a product of two or three numbers. The following equations give aurifeuillean factors for the Cunningham project bases as a product of F, L and M:[3]
If we let L = CD, M = C + D, the aurifeuillean factorizations for bn ± 1 of the form F * (CD) * (C + D) = F * L * M with the bases 2 ≤ b ≤ 24 (perfect powers excluded, since a power of bn is also a power of b) are:
(for the coefficients of the polynomials for all square-free bases up to 199 and up to 998, see [4][5][6])
b Number (CD) * (C + D) = L * M F C D
2 24k + 2 + 1 1 22k + 1 + 1 2k + 1
3 36k + 3 + 1 32k + 1 + 1 32k + 1 + 1 3k + 1
5 510k + 5 - 1 52k + 1 - 1 54k + 2 + 3(52k + 1) + 1 53k + 2 + 5k + 1
6 612k + 6 + 1 64k + 2 + 1 64k + 2 + 3(62k + 1) + 1 63k + 2 + 6k + 1
7 714k + 7 + 1 72k + 1 + 1 76k + 3 + 3(74k + 2) + 3(72k + 1) + 1 75k + 3 + 73k + 2 + 7k + 1
10 1020k + 10 + 1 104k + 2 + 1 108k + 4 + 5(106k + 3) + 7(104k + 2)
+ 5(102k + 1) + 1
107k + 4 + 2(105k + 3) + 2(103k + 2)
+ 10k + 1
11 1122k + 11 + 1 112k + 1 + 1 1110k + 5 + 5(118k + 4) - 116k + 3
- 114k + 2 + 5(112k + 1) + 1
119k + 5 + 117k + 4 - 115k + 3
+ 113k + 2 + 11k + 1
12 126k + 3 + 1 122k + 1 + 1 122k + 1 + 1 6(12k)
13 1326k + 13 - 1 132k + 1 - 1 1312k + 6 + 7(1310k + 5) + 15(138k + 4)
+ 19(136k + 3) + 15(134k + 2) + 7(132k + 1) + 1
1311k + 6 + 3(139k + 5) + 5(137k + 4)
+ 5(135k + 3) + 3(133k + 2) + 13k + 1
14 1428k + 14 + 1 144k + 2 + 1 1412k + 6 + 7(1410k + 5) + 3(148k + 4)
- 7(146k + 3) + 3(144k + 2) + 7(142k + 1) + 1
1411k + 6 + 2(149k + 5) - 147k + 4
- 145k + 3 + 2(143k + 2) + 14k + 1
15 1530k + 15 + 1 1514k + 7 - 1512k + 6 + 1510k + 5
+ 154k + 2 - 152k + 1 + 1
158k + 4 + 8(156k + 3) + 13(154k + 2)
+ 8(152k + 1) + 1
157k + 4 + 3(155k + 3) + 3(153k + 2)
+ 15k + 1
17 1734k + 17 - 1 172k + 1 - 1 1716k + 8 + 9(1714k + 7) + 11(1712k + 6)
- 5(1710k + 5) - 15(178k + 4) - 5(176k + 3)
+ 11(174k + 2) + 9(172k + 1) + 1
1715k + 8 + 3(1713k + 7) + 1711k + 6
- 3(179k + 5) - 3(177k + 4) + 175k + 3
+ 3(173k + 2) + 17k + 1
18 184k + 2 + 1 1 182k + 1 + 1 6(18k)
19 1938k + 19 + 1 192k + 1 + 1 1918k + 9 + 9(1916k + 8) + 17(1914k + 7)
+ 27(1912k + 6) + 31(1910k + 5) + 31(198k + 4)
+ 27(196k + 3) + 17(194k + 2) + 9(192k + 1) + 1
1917k + 9 + 3(1915k + 8) + 5(1913k + 7)
+ 7(1911k + 6) + 7(199k + 5) + 7(197k + 4)
+ 5(195k + 3) + 3(193k + 2) + 19k + 1
20 2010k + 5 - 1 202k + 1 - 1 204k + 2 + 3(202k + 1) + 1 10(203k + 1) + 10(20k)
21 2142k + 21 - 1 2118k + 9 + 2116k + 8 + 2114k + 7
- 214k + 2 - 212k + 1 - 1
2112k + 6 + 10(2110k + 5) + 13(218k + 4)
+ 7(216k + 3) + 13(214k + 2) + 10(212k + 1) + 1
2111k + 6 + 3(219k + 5) + 2(217k + 4)
+ 2(215k + 3) + 3(213k + 2) + 21k + 1
22 2244k + 22 + 1 224k + 2 + 1 2220k + 10 + 11(2218k + 9) + 27(2216k + 8)
+ 33(2214k + 7) + 21(2212k + 6) + 11(2210k + 5)
+ 21(228k + 4) + 33(226k + 3) + 27(224k + 2)
+ 11(222k + 1) + 1
2219k + 10 + 4(2217k + 9) + 7(2215k + 8)
+ 6(2213k + 7) + 3(2211k + 6) + 3(229k + 5)
+ 6(227k + 4) + 7(225k + 3) + 4(223k + 2)
+ 22k + 1
23 2346k + 23 + 1 232k + 1 + 1 2322k + 11 + 11(2320k + 10) + 9(2318k + 9)
- 19(2316k + 8) - 15(2314k + 7) + 25(2312k + 6)
+ 25(2310k + 5) - 15(238k + 4) - 19(236k + 3)
+ 9(234k + 2) + 11(232k + 1) + 1
2321k + 11 + 3(2319k + 10) - 2317k + 9
- 5(2315k + 8) + 2313k + 7 + 7(2311k + 6)
+ 239k + 5 - 5(237k + 4) - 235k + 3
+ 3(233k + 2) + 23k + 1
24 2412k + 6 + 1 244k + 2 + 1 244k + 2 + 3(242k + 1) + 1 12(243k + 1) + 12(24k)
  • Lucas numbers have the following aurifeuillean factorization:[7]
where is the th Lucas number, and is the th Fibonacci number.

History

[edit]

In 1869, before the discovery of aurifeuillean factorizations, Landry [fr; es; de], through a tremendous manual effort,[8][9] obtained the following factorization into primes:

Three years later, in 1871, Aurifeuille discovered the nature of this factorization; the number for , with the formula from the previous section, factors as:[2][8]

Of course, Landry's full factorization follows from this (taking out the obvious factor of 5). The general form of the factorization was later discovered by Lucas.[2]

536903681 is an example of a Gaussian Mersenne norm.[9]

References

[edit]
  1. ^ A. Granville, P. Pleasants (2006). "Aurifeuillian factorization" (PDF). Math. Comp. 75 (253): 497–508. doi:10.1090/S0025-5718-05-01766-7.
  2. ^ a b c d Weisstein, Eric W. "Aurifeuillean Factorization". MathWorld.
  3. ^ "Main Cunningham Tables". At the end of tables 2LM, 3+, 5-, 6+, 7+, 10+, 11+ and 12+ are formulae detailing the aurifeuillean factorizations.
  4. ^ List of aurifeuillean factorization of cyclotomic numbers (square-free bases up to 199)
  5. ^ Coefficients of Lucas C,D polynomials for all square-free bases up to 199
  6. ^ Coefficients of Lucas C,D polynomials for all square-free bases up to 998
  7. ^ Lucas Aurifeuilliean primitive part
  8. ^ a b Integer Arithmetic, Number Theory – Aurifeuillean Factorizations, Numericana
  9. ^ a b Gaussian Mersenne, the Prime Pages glossary
[edit]