a(n) = 2^n + n*(n+3).

Terms

a(0) =1a(1) =6a(2) =14a(3) =26a(4) =44a(5) =72a(6) =118a(7) =198a(8) =344a(9) =620a(10) =1154a(11) =2202a(12) =4276a(13) =8400a(14) =16622a(15) =33038a(16) =65840a(17) =131412a(18) =262522a(19) =524706a(20) =1049036a(21) =2097656a(22) =4194854a(23) =8389206a(24) =16777864a(25) =33555132a(26) =67109618a(27) =134218538a(28) =268436324a(29) =536871840