a(n) = binomial((n+1)^2, n^2).A070781a(n) = binomial((n+1)^2, n^2).Terms a(0) =1a(1) =4a(2) =126a(3) =11440a(4) =2042975a(5) =600805296a(6) =262596783764External referencesoeis: A070781