466048domain: NAppears in sequencesNumber of subsets of {1,2,3,...,n} that sum to 0 mod 9.at n=22A068030Number of subsets of {1,2,3,...,n} that sum to 0 mod 18.at n=23A068039Numbers n for which n = phi(x)*phi(y), where n = x + y and phi(x) is the Euler totient function of x.at n=27A273800