5286126domain: NAppears in sequencesTriangular numbers whose sum of divisors is also a triangular number.at n=7A083674Least n-gonal number greater than 1 such that sigma(n) is also n-gonal.at n=3A259240Triangular numbers n such that psi(n) is also a triangular number, where psi is the Dedekind psi function (A001615).at n=7A292063