a(n) = 2^n + 3n + 1.

Terms

a(0) =2a(1) =6a(2) =11a(3) =18a(4) =29a(5) =48a(6) =83a(7) =150a(8) =281a(9) =540a(10) =1055a(11) =2082a(12) =4133a(13) =8232a(14) =16427a(15) =32814a(16) =65585a(17) =131124a(18) =262199a(19) =524346a(20) =1048637a(21) =2097216a(22) =4194371a(23) =8388678a(24) =16777289a(25) =33554508a(26) =67108943a(27) =134217810a(28) =268435541a(29) =536871000