got it. error of reasoning (worst kind): I restricted myself to subsets of size d|n. Shouldn't have. I stand corrected. Thanks Dan. W. ----- Original Message ----- From: "Daniel Asimov" <dasimov@earthlink.net> To: "math-fun" <math-fun@mailman.xmission.com> Sent: Friday, March 11, 2005 11:40 PM Subject: RE: [math-fun] well posed problem? Wouter Meeussen writes: << of all subsets of the n-th roots of -1, n= 1 to 20, how many add to zero? ?? 0, 1, 1, 3, 1, 6, 1, 11, 4, 8, 1, 50, 1, 10, 9, 107, 1, 240, 1, 316 ?? where are the 'groupies' when you need them?
It appears you have 6 subsets of the 6th roots of unity, but I count 9 subsets (03, 14, 25, 024, 135, 0134, 2350, 3401, 012345). (In any case there could be another sequence based only on minimal such subsets,but it wouldn't be as interesting.) --Dan _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun