a(n) = binomial(2*n+1, n-5).

Terms

a(0) =1a(1) =13a(2) =105a(3) =680a(4) =3876a(5) =20349a(6) =100947a(7) =480700a(8) =2220075a(9) =10015005a(10) =44352165a(11) =193536720a(12) =834451800a(13) =3562467300a(14) =15084504396a(15) =63432274896a(16) =265182149218