206830domain: NAppears in sequencesIndices of pentagonal numbers that are also heptagonal.at n=3A046199Number of n X 3 0..1 arrays with rows and columns lexicographically nondecreasing and every element equal to at least one horizontal or vertical neighbor.at n=18A201348G.f.: 1/(1-x)^4 * Product_{k>=1} (1 + x^k).at n=27A325952