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

A135861

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

Terms

    a(0) =1a(1) =1a(2) =5a(3) =55a(4) =969a(5) =23751a(6) =749398a(7) =28989675a(8) =1329890705a(9) =70625252863

External references