[结论]一些结论

(gcd(2^a – 1, 2^b – 1) = 2^{gcd(a, b)} – 1)
(gcd(fib[a], fib[b]) = fib[gcd(a, b)])
斯特林公式：(n!)约等于(\sqrt{2 · \pi · n} · (\frac e n)^n)
(\pi = 3.14159265358979, e = 2.71828182845905)
a & b <= min(a, b) $$\sum _{i=1}^n{i}^2=\frac{n\cdot (n+1)\cdot (2\cdot n+1)}{6}$$ $$\sum _{i=1}^n{i}^3=(\frac{n\cdot (n+1)}{2}{)}^2$$