221223domain: NAppears in sequencesLucky numbers that are concatenations of n with n + 2.at n=23A032652Numbers k such that phi(6k) is either phi(6k-2) or phi(6k+2), where phi is Euler's totient function A000010.at n=36A279011Numbers k such that phi(6k) = phi(6k+2), where phi is Euler's totient function A000010.at n=17A279184