円周率の近似
1 π = 12 ∑ n = 0 ∞ ( − 1 ) n ( 6 n ) ! ( 3 n ) ! ( n ! ) 3 13591409 + 545140134 n 640320 3 n + 3 2 {\displaystyle {\frac {1}{\pi }}=12\sum _{n=0}^{\infty }{\frac {{(-1)}^{n}(6n)!}{(3n)!{(n!)}^{3}}}{\frac {13591409+545140134n}{{640320}^{3n+{\frac {3}{2}}}}}}