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

Terms

a(0) =1a(1) =5a(2) =37a(3) =299a(4) =2517a(5) =21700a(6) =190051a(7) =1683218a(8) =15033173a(9) =135142796a(10) =1221246132a(11) =11083374659a(12) =100946732307a(13) =922205369324