202650domain: NAppears in sequencesNumber of quadrilaterals in a triangular matchstick arrangement of side n.at n=28A204185Least positive integer k such that (k-1)^2+(k*n)^2, k^2+(k*n-1)^2, (k+1)^2+(k*n)^2 and k^2+(k*n+1)^2 are all prime.at n=47A261382a(n) = 2^n * n! * [x^n] (-1/2 - exp(-x))^n.at n=5A375541