MathDB
Sequence has finitely many composite numbers

Source: Kvant Magazine No. 6 2021 M2656

March 9, 2023
number theoryKvant

Problem Statement

The increasing sequence of natural numbers a1,a2,a_1,a_2,\ldots is such that for every n>100n>100 the number ana_n is equal to the smallest natural number greater than an1a_{n-1} and not divisible by any of the numbers a1,,an1a_1,\ldots,a_{n-1}. Prove that there is only a finite number of composite numbers in such a sequence.
Proposed by P. Kozhevnikov