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

Terms

a(0) =1a(1) =3a(2) =17a(3) =105a(4) =641a(5) =3873a(6) =23297a(7) =139905a(8) =839681a(9) =5038593a(10) =30232577a(11) =181397505a(12) =1088389121a(13) =6530342913a(14) =39182073857a(15) =235092475905