34479domain: NAppears in sequencesNumbers k such that 139*2^k-1 is prime.at n=39A050595Numbers k such that phi(k)+sigma(k) is a perfect cube.at n=23A061366a(n) = 6*a(n-1) - 3*a(n-2) for n > 1; a(0) = 1, a(1) = 7.at n=6A164550a(n) = Sum_{k=1..n-1} k^2*phi(k) + n^2*phi(n)/2, where phi = A000010.at n=20A333293