Question 21
Consider the sequence $ a_1, a_2, \ldots $ defined by
$$ a_{n}=2^{n}+3^{n}+6^{n}-1\quad(n=1,2,\cdots). $$
Determine all positive integers that are relatively prime to every term of the sequence.
$$ a_{n}=2^{n}+3^{n}+6^{n}-1\quad(n=1,2,\cdots). $$
Determine all positive integers that are relatively prime to every term of the sequence.