# Count Count Count

Discrete Mathematics Level 5

Find the number of ordered septuples of non-negative integers $$\left(x_1, x_2, x_3, x_4, x_5,x_6,x_7\right)$$ such that $$0\le x_i\le 7$$ for all $$i$$ and $$5$$ divides $$\displaystyle \sum_{i=1}^7 3^{x_i}$$.

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