375162560801domain: NAppears in sequencesa(n) = 17^n*cos(2*n*arctan(1/4)) or denominator of tan(2*n*arctan(1/4)).at n=9A067361Values of x such that x^2 + y^2 = 17^n with x and y coprime and 0 < x < y.at n=19A230622