Number of subsets of {1,2,3,...,n} that sum to 0 mod 7.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =5a(6) =10a(7) =20a(8) =38a(9) =74a(10) =146a(11) =294a(12) =586a(13) =1172a(14) =2344a(15) =4684a(16) =9364a(17) =18724a(18) =37452a(19) =74900a(20) =149800a(21) =299600a(22) =599192a(23) =1198376a(24) =2396744a(25) =4793496a(26) =9586984a(27) =19173968a(28) =38347936a(29) =76695856