IMO 1985 LL BUL11

Let a and b be integers and n a positive integer. Prove that

imolonglistmathematicsolympiad

IMO 1985 LL BUL11

Origin: BUL

Problem

Let a and b be integers and n a positive integer. Prove that bn−1a(a + b)(a + 2b) \cdot \cdot \cdot (a + (n −1)b) n! is an integer.