# Freaky Factorials

Number Theory Level 4

$\large n!(n-1)!=m!$

Solve the equation above for natural numbers $$m,n$$.

Let $$S = \{ (m_1, n_1), (m_2, n_2), \ldots, (m_j, n_j) \}$$ denote all the possible solutions.

Evaluate $$\displaystyle \sum_{k=1}^j (m_k + n_k)$$.

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