[Haskell-cafe] ANN: Math.OEIS 0.1

[Henning Thielemann]

On Mon, 22 Oct 2007, Brent Yorgey wrote:

> Hi all,
>
> I'm pleased to announce the release of a somewhat silly -- yet perhaps
> somewhat useful -- library module,
> Math.OEIS<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/oeis-0.1>,
> intended for the enjoyment of combinatorial dilettantes, Project Euler
> addicts, and the merely curious alike.  It provides a Haskell interface to
> the Online Encyclopedia of Integer Sequences, with support for looking up
> sequences by ID number or partial list.  You can use it to look up any and
> all information on a sequence (references, formulas, comments, keywords...),
> or just return the sequence data as a list.  My favorite feature -- and the
> initial impetus for the library -- is that it can "guess" the rest of a
> sequence by using the first search result from the OEIS to extend it.  Some
> examples of use:
>
> Prelude Math.OEIS> extendSequence [5,7,11,13,17]
> [5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71...

Cute!

> Prelude Math.OEIS> extendSequence [2,4,8,16,32]
> [2,4,8,16,32,64,128,256,512,1024,2048,4096,8192...
>
> Prelude Math.OEIS> description `fmap` lookupSequence [1,2,5,14,42]
> Just "Catalan numbers: C(n) = binomial(2n,n)/(n+1) = (2n)!/(n!(n+1)!). Also
> called Segner numbers."

The Online Encyclopedia of Integer Sequences should really contain more
Haskell code for describing the sequences.