935387159850domain: NAppears in sequencesa(n) = (20*n)!*(3*n)!/((10*n)!*(9*n)!*(4*n)!).at n=2A295475a(n) = (10*n)!*(3*n/2)!/((5*n)!*(9*n/2)!*(2*n)!).at n=4A364181