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

A299428

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

Terms

    a(0) =1a(1) =4a(2) =63a(3) =1872a(4) =82775a(5) =4874688a(6) =358919022a(7) =31726703424

External references