244572domain: NAppears in sequencesNumbers k such that sigma(sigma(k)) == phi(k) (mod sigma(k)).at n=30A067204Number of 9 X 9 arrays of squares of integers, symmetric under 90-degree rotation, with all rows summing to n.at n=21A156401G.f. satisfies: A(x) = 1 + x^2 + x^2*A'(x)/A(x).at n=10A245119