Question 174
For a positive integer $x$, let $f(x)$ be the last two digits of $x$. Find
$$
\sum_{n=1}^{2019} f\left(7^{7^{n}}\right).
$$
$$
\sum_{n=1}^{2019} f\left(7^{7^{n}}\right).
$$
MathNet 2019-part-04 — 184 problems (EN–VI) Question 174
Math Olympiad Vault · MathNet 2019-part-04 — 184 problems (EN–VI)