Incenter and circumcenter of triangle

Given an integer sided triangle ABC: Let I be the incenter of ABC. Let D be the intersection between the line AI and the circumcircle of ABC (A ≠ D).

We define F(L) as the sum of BC for the triangles ABC that satisfy AC = DI and BC ≤ L.

For example, F(15) = 45 because the triangles ABC with (BC,AC,AB) = (6,4,5), (12,8,10), (12,9,7), (15,9,16) satisfy the conditions.

Find F(10⁹).

Written by gamwe6 who lives and works in San Francisco building useful things. You should follow him on Twitter