Number of subsets of {1,2,3,...,n} that sum to 0 mod 18.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =3a(7) =8a(8) =16a(9) =30a(10) =58a(11) =115a(12) =229a(13) =456a(14) =912a(15) =1824a(16) =3643a(17) =7286a(18) =14572a(19) =29132a(20) =58262a(21) =116522a(22) =233024a(23) =466048a(24) =932096a(25) =1864150a(26) =3728300a(27) =7456600a(28) =14913112a(29) =29826220