Requirement for an even permutation to be a square

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Given an even permutation $\sigma,$ what more is required for it to be the square of some other permutation? Is it enough that there be an even number of transpositions in its cycle decomposition?

I looked at the case $\sigma=(12)(3456)$ and could not find a squareroot for that, or others I tried having an odd number of transpositions in their decompositions.

I would be interested in any specific counterexample having an odd number of transpositions, and also whether more is required for a permutation to be a square.