$7^{7^n}+1$ is the product of at least $2n + 3$ primes
Source: USAMO 2007
April 26, 2007
AMCUSA(J)MOUSAMOinductionsymmetryalgebrapolynomial
Problem Statement
Prove that for every nonnegative integer , the number is the product of at least (not necessarily distinct) primes.