Talk:Bell number

I've added a section on calculating Bell numbers that doesn't use any equations; I think pictures like this are more accessible than descriptions which use a lot of equations (people have also complained about the typeface we use for math; see, for example, the discussion over at JPEG). Samboy 04:38, 16 May 2005 (UTC)

I've put the algorithm after the "theoretical" material; it seems of lesser interest. Michael Hardy 21:03, 16 May 2005 (UTC)

One of my goals when making those additions is to present Bell numbers so that an intelligent elementry school kid can understand and even calculate them. Of course, what I really need to do is add a picture showing the Bell number combining three numbers together (or even have pictures of labelled balls in boxes). I've added some section headers so that people can go from section to section quickly; this hopefully makes the article more readable. Samboy 01:11, 17 May 2005 (UTC)

Requested move

The following discussion is an archived debate of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the debate was: it was moved—jiy (talk) 18:40, 8 January 2006 (UTC)

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I know currently more pages link to the plural than the singular. but for pages about kinds of numbers (Fibonacci number, Catalan number, highly totient number, etc.) their usually at the singular. Numerao 18:38, 20 September 2005 (UTC)

• I support this; it has the practical advantage that the plural [[Bell number]]s can link to the singular without piping or redirection; the reverse is not true. Septentrionalis 19:40, 21 September 2005 (UTC)
• I also support the proposed move, for the same reason as ibid. PrimeFan 17:55, 11 October 2005 (UTC)

Such titles should be plural when the sequence of numbers is what is of interest. In the case of prime number or perfect number, the concept is of interest when thinking about a particular number and not just when thinking about a sequence of numbers. This distinction seems fairly clear-cut when thinking about polynomial sequence (it is appropriate that the article title Hermite polynomials is plural while Bernstein polynomial is not). Maybe it's a bit less clear-cut with sequences of numbers, but we need to talk about it. Michael Hardy 00:34, 22 September 2005 (UTC)

From a Handbook of Integer Sequences viewpoint, "Bell numbers" is of greater interest. From a Dictionary of Curious Integers viewpoint, "Bell number" is of greater interest. PrimeFan 17:55, 11 October 2005 (UTC)

The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Empty set

Surely there can be no partitions of an empty set.

If we permit {} to be a partition of {}, then there are an infinite number of partitions of {X}: { {X} }, { {X}, {} }, { {X}, {}, {} } and so on.

The situation is ananlagous to the reason why we do not count 1 as a prime number, because if we did then there would be more than one way to break any number up into prime factors. Indeed, the factorisations of any number are prescisely the ways of dividing up it's set of prime factors into partitions.