a(n) = 12*a(n-2) - 25*a(n-4) with initial terms 1,6,17,47.

Terms

a(0) =1a(1) =6a(2) =17a(3) =47a(4) =179a(5) =414a(6) =1723a(7) =3793a(8) =16201a(9) =35166a(10) =151337a(11) =327167a(12) =1411019a(13) =3046854a(14) =13148803a(15) =28383073a(16) =122510161a(17) =264425526a(18) =1141401857a(19) =2463529487a(20) =10634068259a(21) =22951715694a(22) =99073772683a(23) =213832351153a(24) =923033565721