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

Terms

a(0) =24a(1) =74a(2) =228a(3) =698a(4) =2124a(5) =6434a(6) =19428a(7) =58538a(8) =176124a(9) =529394a(10) =1590228a(11) =4774778a(12) =14332524a(13) =43013954a(14) =129074628a(15) =387289418a(16) =1161999324a(17) =3486260114a(18) =10459304628a(19) =31378962458a(20) =94138984524a(21) =282421147874a(22) =847271832228