[seqfan] Re: Modular Partitions
jean-paul allouche
jean-paul.allouche at imj-prg.fr
Fri May 2 07:29:42 CEST 2014
Hi, I suspect the following paper might help:
http://dx.doi.org/10.1016/0012-365X(86)90089-0
best wishes
jean-paul
Le 02/05/14 04:03, franktaw at netscape.net a écrit :
> Number of necklaces with n+k beads, n white and k black? I'm pretty
> sure that's right, though I don't see how to prove it.
>
> Franklin T. Adams-Watters
>
> -----Original Message-----
> From: Jens Voß <jens at voss-ahrensburg.de>
>
> Hi there, sequence fans,
>
> I was playing around with what I call "modular partition numbers":
> Essentially different ways to write the neutral element of the group
> Z/nZ as a sum of length k (for given n, k > 0).
>
> For example, for n = 5 and k = 4, we have thepartitions
>
> 0+0+0+0 = 0
> 0+0+1+4 = 5 = 0
> 0+0+2+3 = 5 = 0
> 0+1+1+3 = 5 = 0
> 0+1+2+2 = 5 = 0
> 0+2+4+4 = 10 = 0
> 0+3+3+4 = 10 = 0
> 1+2+3+4 = 10 = 0
> 1+3+3+3 = 10 = 0
> 3+4+4+4 = 15 = 0
>
> so the number of 5-modular partitions of length 4 is 10.
>
> I computed the the values for n + k < 20 (as a square array read by
> antidiagonals), and was somewhat surprised that this sequence isn't yet
> in the database (even though several of the rows resp. columns are).
> However, I was even more surprised to find that the array is symmetric
> in n and k:
>
> 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
> 1 1 1 1
> 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8
> 9 9 10
> 1 2 4 5 7 10 12 15 19 22 26 31 35 40 46
> 51 57
> 1 3 5 10 14 22 30 43 55 73 91 116 140 172 204
> 245
> 1 3 7 14 26 42 66 99 143 201 273 364 476 612 776
> 1 4 10 22 42 80 132 217 335 504 728 1038 1428 1944
> 1 4 12 30 66 132 246 429 715 1144 1768 2652 3876
> 1 5 15 43 99 217 429 810 1430 2438 3978 6310
> 1 5 19 55 143 335 715 1430 2704 4862 8398
> 1 6 22 73 201 504 1144 2438 4862 9252
> 1 6 26 91 273 728 1768 3978 8398
> 1 7 31 116 364 1038 2652 6310
> 1 7 35 140 476 1428 3876
> 1 8 40 172 612 1944
> 1 8 46 204 776
> 1 9 51 245
> 1 9 57
> 1 10
> 1
>
> I haven't been able to come up with a formula for the numbers (neither
> recursive nor direct), and I don't see an immediate reason for the
> symmetry either (some sort of dualism). Can somebody find a formula or
> explain why the array is symmetric?
>
> Best regards,
> Jens
>
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