930257069563domain: NAppears in sequencesa(n) = (4*n + 1)^(1/2)/(4*n + 1)*((1 - p)*q^n - (1 - q)*p^n), where p = (1 - (4*n + 1)^(1/2))/2 and q = (1 + (4*n + 1)^(1/2))/2.at n=17A171180a(n) = hypergeom([1/2 - n/2, -n/2], [-n], -72).at n=18A350469