A068012 Number of subsets of {1,2,3,...,n} that sum to 0 mod 6.

1, 1, 1, 2, 3, 6, 12, 22, 44, 88, 172, 344, 688, 1368, 2736, 5472, 10928, 21856, 43712, 87392, 174784, 349568, 699072, 1398144, 2796288, 5592448, 11184896, 22369792, 44739328, 89478656, 178957312, 357914112, 715828224, 1431656448, 2863311872, 5726623744

Offset: 0

Author

Antti Karttunen, Feb 11 2002

Keywords

• nonn

Crossrefs

6th row of A068009.

Programs

Maple

b:= proc(n, s) option remember; `if`(n=0, `if`(s=0, 1, 0),
      b(n-1, s)+b(n-1, irem(s+n, 6)))
    end:
a:= n-> b(n, 0):
seq(a(n), n=0..35);  # Alois P. Heinz, May 02 2025

Formula

Empirical G.f.: (x-1)*(2*x^4+3*x^3+x^2-1) / ((2*x-1)*(2*x^3-1)). - Colin Barker, Dec 22 2012