113550domain: NAppears in sequencesG.f. satisfies: a(n) = [x^n] ( A(x)^n + 1/A(x)^n ) for n>1, with a(0)=a(1)=1.at n=5A237644Numbers k such that sigma(phi(k)) - phi(k) = phi(sigma(k)), where phi(k) is the Euler totient function of k and sigma(k) is the sum of the divisors of k.at n=18A271633