571538domain: NAppears in sequencesa(n) = 9*a(n-1) + a(n-2), starting with a(0) = 2 and a(1) = 9.at n=6A087798Twice Chebyshev polynomials of the first kind, T(n,x), evaluated at 83/2.at n=3A099373Number of corona for a hexagon of edge n with diamonds of side 1.at n=8A380346