a(n) = 3*a(n-1) + 2*3^n - 1, a(0) = 0.

Terms

a(0) =0a(1) =5a(2) =32a(3) =149a(4) =608a(5) =2309a(6) =8384a(7) =29525a(8) =101696a(9) =344453a(10) =1151456a(11) =3808661a(12) =12488864a(13) =40655237a(14) =131531648a(15) =423292757a(16) =1355971712a(17) =4326195461a(18) =13753427360a(19) =43584805013a(20) =137727983840a(21) =434104657925