559902916domain: NAppears in sequencesTriangular numbers that are 1/6 of another triangular number.at n=10A077289Positive triangular numbers (A000217) that are pentagonal numbers (A000326) divided by 2.at n=4A259156Positive hexagonal numbers (A000384) that are pentagonal numbers (A000326) divided by 2.at n=2A259162