G.f.: Sum_{n>=0} (4 + x^n)^n * x^n / (1-x)^(n+1).

Terms

a(0) =1a(1) =5a(2) =26a(3) =127a(4) =636a(5) =3153a(6) =15727a(7) =78406a(8) =391494a(9) =1955563a(10) =9772721a(11) =48847892a(12) =244196337a(13) =1220857221a(14) =6103941997a(15) =30518746918a(16) =152591088797a(17) =762948154799