(1/9) times the sum of the elements of all subsets of [n] whose sum is divisible by nine.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =1a(5) =3a(6) =9a(7) =23a(8) =60a(9) =150a(10) =354a(11) =843a(12) =1983a(13) =4608a(14) =10638a(15) =24318a(16) =55043a(17) =123862a(18) =276868a(19) =614996a(20) =1359446a(21) =2990726a(22) =6550528a(23) =14292132a(24) =31069860a(25) =67316446a(26) =145403700a(27) =313177200a(28) =672746880a(29) =1441600632