37162384domain: NAppears in sequencesa(n) = Sum_{k=0..n} (-1)^(n-k) C(n,k)*C(k^2,n).at n=7A003235Consider the family of directed graphs with loops. Sequence gives the triangle read by rows giving coefficients of polynomials arising from enumeration of those graphs on n arcs and loops.at n=40A098267