a(n) = ((-1)^n*5^(n+1) + 9^(n+1))/14.

Terms

a(0) =1a(1) =4a(2) =61a(3) =424a(4) =4441a(5) =36844a(6) =347221a(7) =3046864a(8) =27812401a(9) =248358484a(10) =2244991981a(11) =20156099704a(12) =181649037961