Number of subsets of {1,2,3,...,n} that sum to 0 mod 9.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =2a(5) =4a(6) =8a(7) =15a(8) =30a(9) =60a(10) =116a(11) =230a(12) =458a(13) =912a(14) =1824a(15) =3648a(16) =7286a(17) =14572a(18) =29144a(19) =58264a(20) =116524a(21) =233044a(22) =466048a(23) =932096a(24) =1864192a(25) =3728300a(26) =7456600a(27) =14913200a(28) =29826224a(29) =59652440