63453domain: NAppears in sequencesa(n) = n*(2*n^2 + 5*n + 17)/2.at n=39A163661Number of vertices in an equilateral triangle "frame" of size n (see Comments in A328526 for definition).at n=19A333031a(n) = (3*n-1)*(n^4-18*n^3+179*n^2-582*n+720)/120.at n=21A381193