a(n) = Sum_{k=0..floor(n/2)} binomial(n+k-1,k) * binomial(n+k-1,n-2*k).

A387301

a(n) = Sum_{k=0..floor(n/2)} binomial(n+k-1,k) * binomial(n+k-1,n-2*k).

Terms

    a(0) =1a(1) =0a(2) =2a(3) =9a(4) =34a(5) =140a(6) =587a(7) =2471a(8) =10490a(9) =44829a(10) =192532a(11) =830368a(12) =3594031a(13) =15602873a(14) =67913841a(15) =296276639a(16) =1295096906a(17) =5671183187a(18) =24873020345a(19) =109243716358a(20) =480415979564

External references