MathDB

2014-2015 Spring OMO #8

Source:

April 14, 2015

Online Math Open

Problem Statement

Determine the number of sequences of positive integers

1 = x_0 < x_1 < \dots < x_{10} = 10^{5}

with the property that for each

m=0,\dots,9

the number

\tfrac{x_{m+1}}{x_m}

is a prime number.
Proposed by Evan Chen