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Ira Gessel
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The exponential generating function for permutations of order dividing $k$ is $$\exp\biggl(\sum_{d\mid k} \frac{x^d}{d}\biggr).$$ These are permutations in which every cycle length divides $k$. You can find the exponential generating function for permutations of order $k$ from this by M"obius inversion; there won't be a simpler formula.

Ira Gessel
  • 17k
  • 1
  • 58
  • 80