171667domain: NAppears in sequencesNumbers k such that phi(sigma(phi(k))) = sigma(k).at n=16A066462Sum of piles of first n primes: a(n) = Sum(prime(i)*(2*i-1): 1<=i<=n).at n=39A316322a(n) = Sum_{k=1..n} binomial(n,k) * sigma(k) * sigma(n - k + 1), where sigma = A000203.at n=10A330088