1462552domain: NAppears in sequencesa(n) = ( (7 + sqrt(7))^n - (7 - sqrt(7))^n )/(2*sqrt(7)).at n=6A154248Numbers n such that sigma(n)/phi(n) = 25/4, where sigma = A000203, phi = A000010.at n=20A165629a(0) = 0; a(n) = ( (n + sqrt(n))^n - (n - sqrt(n))^n )/(2 * sqrt(n)).at n=7A360766