701260565domain: NAppears in sequencesa(n) = 5*a(n-1) - a(n-2), with a(0) = 2, a(1) = 5.at n=13A003501Numerators of continued fraction convergents to sqrt(21).at n=25A041032Array T(n,k) read by antidiagonals: T(n,k) = sum(i=0...n, (-1)^(n+i) * C(n+i,2i) * n/(2i+1) * k^(2i+1) ), n>0, k>1.at n=39A231123