a(n) = Sum_{k=1..n} k^3 * 4^(n-k).

Terms

a(0) =0a(1) =1a(2) =12a(3) =75a(4) =364a(5) =1581a(6) =6540a(7) =26503a(8) =106524a(9) =426825a(10) =1708300a(11) =6834531a(12) =27339852a(13) =109361605a(14) =437449164a(15) =1749800031a(16) =6999204220a(17) =27996821793a(18) =111987293004a(19) =447949178875