A068042 - OEIS

%I #6 Sep 08 2022 13:17:12

%S 1,1,1,1,1,1,2,6,14,26,49,99,197,391,782,1564,3123,6244,12490,24970,

%T 49940,99880,199738,399472,798940,1597844,3195684,6391368,12782668,

%U 25565336,51130664,102261174,204522354,409044702,818089110,1636178220

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

%F 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]

%Y 21st row of A068009.

%K nonn

%O 0,7

%A _Antti Karttunen_, Feb 11 2002