Question 128
Consider the sequence $a_1, a_2, \dots$ defined by
$$
a_n = 2^n + 3^n + 6^n - 1.
$$
for all positive integers $n$. Determine all positive integers that are relatively prime to every term of the sequence.
$$
a_n = 2^n + 3^n + 6^n - 1.
$$
for all positive integers $n$. Determine all positive integers that are relatively prime to every term of the sequence.