A068042 - OEIS

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

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OFFSET

0,7

LINKS

Table of n, a(n) for n=0..35.

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]

CROSSREFS

21st row of A068009.

Sequence in context: A138318 A212964 A279742 * A068041 A182155 A101586

Adjacent sequences: A068039 A068040 A068041 * A068043 A068044 A068045

KEYWORD

nonn

AUTHOR

Antti Karttunen, Feb 11 2002

STATUS

approved