2 a b − 1 = ( 2 a − 1 ) ( 2 a ( b − 1 ) + 2 a ( b − 2 ) + . . . + 2 a + 1 ) {\displaystyle 2^{ab}-1=(2^{a}-1)(2^{a(b-1)}+2^{a(b-2)}+...+2^{a}+1)}
let p ( x ) = x n + a n − 1 x n − 1 + a n − 2 x n − 2 + . . . + a 0 = ( x − r 1 ) ( x − r 2 ) ⋯ ( x − r n ) {\displaystyle p(x)=x^{n}+a_{n-1}x^{n-1}+a_{n-2}x^{n-2}+...+a_{0}=(x-r_{1})(x-r_{2})\cdots (x-r_{n})} then a k = ( − 1 ) n − k ∑ 1 ≤ i 1 < i 2 < . . . < i k ≤ n r 1 r 2 ⋯ r n r i 1 r i 2 ⋯ r i k {\displaystyle a_{k}=(-1)^{n-k}\sum _{1\leq i_{1}<i_{2}<...<i_{k}\leq n}{\frac {r_{1}r_{2}\cdots r_{n}}{r_{i_{1}}r_{i_{2}}\cdots r_{i_{k}}}}}
