153295domain: NAppears in sequencesNumber of upward triangles in a Star of David matchstick arrangement of size n.at n=31A045950Number of n-vertex, 2-edge multigraphs that are not nesting. Number of n-vertex, 2-edge multigraphs that are not crossing.at n=31A326278a(n) = Sum_{k=1..n} tan(k*Pi/(1+2*n))^4.at n=15A377858