201588domain: NAppears in sequencesG.f. A(x) satisfies: A(x) = x + x^2 * exp(3 * Sum_{k>=1} A(x^k) / k).at n=11A345241Numbers k such that sigma(k + sigma(k)) = sigma(k) + sigma(sigma(k)), where sigma = A000203.at n=4A376831