Skip to content

Number leaving remainder n-1 on division by each n

Question

Find the smallest positive integer xx such that dividing xx by nn leaves remainder n−1n-1 for every n=2,3,…,10n=2,3,\dots,10.

Short answer

2519. The conditions say x≡−1(modn)x\equiv-1 \pmod n for each nn, i.e. x+1x+1 is a multiple of every number from 22 to 1010. The least such multiple is lcm⁡(2,…,10)=2520\operatorname{lcm}(2,\dots,10)=2520, so x=2519x=2519.

Adapted from OpenQuant; question and answer rewritten by SelfMadeQuant.com.

See the hint and the full worked solution in the question bank (free account).

Open the worked solution