大数分解与素性判别有相当关联，一个超过78位数字大数即便在现代电脑也难以分解。[1][2]
已知 n = p q {\displaystyle n=pq}
则 q = 1 − ( ( p − 2 n ) 2 p − n + p p − n ) 2 4 p {\displaystyle q=1-{\frac {{\bigg (}{\sqrt {\frac {(p-2n)^{2}}{p-n}}}+{\frac {p}{\sqrt {p-n}}}{\bigg )}^{2}}{4p}}}
