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

A091144

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

Terms

    a(0) =1a(1) =1a(2) =2a(3) =12a(4) =140a(5) =2530a(6) =62832a(7) =1997688a(8) =77652024a(9) =3573805950a(10) =190223180840

External references