A068042 Number of subsets of {1,2,3,...,n} that sum to 0 mod 21.

1, 1, 1, 1, 1, 1, 2, 6, 14, 26, 49, 99, 197, 391, 782, 1564, 3123, 6244, 12490, 24970, 49940, 99880, 199738, 399472, 798940, 1597844, 3195684, 6391368, 12782668, 25565336, 51130664, 102261174, 204522354, 409044702, 818089110, 1636178220

Offset: 0

Author

Antti Karttunen, Feb 11 2002

Keywords

• nonn

Crossrefs

21st row of A068009.

Formula

Empirical G.f.: -(8*x^31 -8*x^28 +4*x^27 -2*x^26 -2*x^25 -6*x^24 +4*x^23 +4*x^22 +2*x^21 +2*x^20 +6*x^19 -8*x^18 -12*x^17 -5*x^16 +6*x^15 +10*x^14 +x^13 -x^12 +5*x^11 +x^10 -6*x^8 -2*x^7 -2*x^6 -x^5 -x^4 +3*x^3 +x^2 +x -1) / ((2*x -1)*(2*x^3 -1)*(2*x^7 -1)*(2*x^21 -1)). [Colin Barker, Dec 22 2012]