a(n) = 3*a(n-1) + 4*a(n-2) for n>1, a(0)=2, a(1)=3.

Terms

a(0) =2a(1) =3a(2) =17a(3) =63a(4) =257a(5) =1023a(6) =4097a(7) =16383a(8) =65537a(9) =262143a(10) =1048577a(11) =4194303a(12) =16777217a(13) =67108863a(14) =268435457a(15) =1073741823a(16) =4294967297a(17) =17179869183a(18) =68719476737a(19) =274877906943