2^n minus the number of partitions of n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =11a(5) =25a(6) =53a(7) =113a(8) =234a(9) =482a(10) =982a(11) =1992a(12) =4019a(13) =8091a(14) =16249a(15) =32592a(16) =65305a(17) =130775a(18) =261759a(19) =523798a(20) =1047949a(21) =2096360a(22) =4193302a(23) =8387353a(24) =16775641a(25) =33552474a(26) =67106428a(27) =134214718a(28) =268431738a(29) =536866347