a(n) = binomial(n + 3, 3)*9^n.

Terms

a(0) =1a(1) =36a(2) =810a(3) =14580a(4) =229635a(5) =3306744a(6) =44641044a(7) =573956280a(8) =7102708965a(9) =85232507580a(10) =997220338686