a(n) = 234*2^n - 120.

Terms

a(0) =114a(1) =348a(2) =816a(3) =1752a(4) =3624a(5) =7368a(6) =14856a(7) =29832a(8) =59784a(9) =119688a(10) =239496a(11) =479112a(12) =958344a(13) =1916808a(14) =3833736a(15) =7667592a(16) =15335304a(17) =30670728a(18) =61341576a(19) =122683272a(20) =245366664a(21) =490733448a(22) =981467016a(23) =1962934152a(24) =3925868424a(25) =7851736968a(26) =15703474056a(27) =31406948232a(28) =62813896584a(29) =125627793288