a(n) = 2*3^n - 2^(n-1) (n>=1).

Terms

a(0) =5a(1) =16a(2) =50a(3) =154a(4) =470a(5) =1426a(6) =4310a(7) =12994a(8) =39110a(9) =117586a(10) =353270a(11) =1060834a(12) =3184550a(13) =9557746a(14) =28681430a(15) =86060674a(16) =258214790a(17) =774709906a(18) =2324260790a(19) =6973044514a(20) =20919657830a(21) =62760022066a(22) =188282163350a(23) =564850684354