a(n) = 2^(n+1) + n^2 - 1.

Terms

a(0) =1a(1) =4a(2) =11a(3) =24a(4) =47a(5) =88a(6) =163a(7) =304a(8) =575a(9) =1104a(10) =2147a(11) =4216a(12) =8335a(13) =16552a(14) =32963a(15) =65760a(16) =131327a(17) =262432a(18) =524611a(19) =1048936a(20) =2097551a(21) =4194744a(22) =8389091a(23) =16777744a(24) =33555007a(25) =67109488a(26) =134218403a(27) =268436184a(28) =536871695a(29) =1073742664