atan(2*x)*log(4)
2*log(4) -------- 2 1 + 4*x
-16*x*log(4) ------------ 2 / 2\ \1 + 4*x /
/ 2 \ | 16*x | 16*|-1 + --------|*log(4) | 2| \ 1 + 4*x / ------------------------- 2 / 2\ \1 + 4*x /