a(n) = binomial(n^2, n)/(n+1).A177234a(n) = binomial(n^2, n)/(n+1).Terms a(0) =2a(1) =21a(2) =364a(3) =8855a(4) =278256a(5) =10737573a(6) =491796152a(7) =26088783435External referencesoeis: A177234