3

Part of 2017 Greece JBMO TST

Problems(1)

7^{2n} -48^n - 1 is always divisible by 9

Source: Greece JBMO TST 2017, Problem 3

Prove that for every positive integer

n

A_n = 7^{2n} -48n - 1

is a multiple of

9

number theoryDivisibility