a(n) = 6*a(n-1) - 8*a(n-2) for n > 1; a(0) = 3, a(1) = 14.

Terms

a(0) =3a(1) =14a(2) =60a(3) =248a(4) =1008a(5) =4064a(6) =16320a(7) =65408a(8) =261888a(9) =1048064a(10) =4193280a(11) =16775168a(12) =67104768a(13) =268427264a(14) =1073725440a(15) =4294934528a(16) =17179803648a(17) =68719345664a(18) =274877644800