a(n) = Sum_{k=0..n} binomial(4*n+3,k).

Terms

a(0) =1a(1) =8a(2) =67a(3) =576a(4) =5036a(5) =44552a(6) =397594a(7) =3572224a(8) =32267668a(9) =292750368a(10) =2665685155a(11) =24347665728a(12) =222972599812