How many points

For real numbers a, k > 0.0; let F(a,k) denote the number of lattice points inside the OAB tringle with the following vertices: O(0.0,0.0) A(a,0.0) B(0.0,k*a) For example: F(5.0,5.0)=81 For O(0.0,0.0), A(5.0,0.0), B(0.0,25.0) What is F(10^16+1,2/(sqrt(5)+1))? [My timing: 1s]