6665999domain: NAppears in sequencesa(n) = 5*a(n-1) - a(n-2) for n > 1, a(0) = 0, a(1) = 1.at n=11A004254Denominators of continued fraction convergents to sqrt(21).at n=21A041033Denominators in continued fraction [0; 1, 3, 1, 3, 1, 3, ...].at n=20A136211Bisection of Chebyshev {S(n, 5)}_{n>=0}; the even part.at n=5A362357