[seqfan] Re: Modular Partitions
franktaw at netscape.net
franktaw at netscape.net
Fri May 2 14:15:41 CEST 2014
The sequence for necklaces, offset 0, is in A047996. I have created
A241926, which is the table of the number of necklaces, offset 1. I
think A047996 ought to be the main sequence for this.
I'm holding off on tying A047996 to Jens's problem. I still don't see a
proof of equivalence, although the numerical evidence is convincing. If
no proof is forthcoming soon, I will put it in as a conjecture.
Franklin T. Adams-Watters
-----Original Message-----
From: franktaw <franktaw at netscape.net>
To: seqfan <seqfan at list.seqfan.eu>
Sent: Thu, May 1, 2014 9:03 pm
Subject: [seqfan] Re: Modular Partitions
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
_______________________________________________
Seqfan Mailing list - http://list.seqfan.eu/
_______________________________________________
Seqfan Mailing list - http://list.seqfan.eu/
More information about the SeqFan
mailing list