IMO 1977 SL 10

Let n be an integer greater than 2. Define V = {1 + kn |

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IMO 1977 SL 10

Origin: NET

Problem

Let n be an integer greater than 2. Define V = {1 + kn | k = 1, 2, . . . }. A number p \inV is called indecomposable in V if it is not possible to find numbers q1, q2 \inV such that q1q2 = p. Prove that there exists a number N \inV that can be factorized into indecomposable factors in V in more than one way.