MathNet 2020 — Math Olympiad Vault — Part 01 Question 26

The integer $202020$ is a multiple of $91$. For every positive integer $n$, show how $n$ additional $2$'s may be inserted into the digits of $202020$ so that the resulting $(n+6)$-digit integer is also a multiple of $91$. For example, a possible way to do this when $n=5$ is $22020220222$ (the inserted $2$'s are underlined).

Formatting note: the retrieved source does not preserve the underlining referenced in this example.