16831644835domain: NAppears in sequencesa(n) = 5*a(n-1) - a(n-2) for n > 1, a(0) = 0, a(1) = 1.at n=16A004254Recurrence equation: a(0) = 1 and a(n) = a(n-1)*sqrt(21*a(n-1)^2 + 4) for n >= 1.at n=4A230338