Permutation group sending even to even and odd to odd
Solution 1:
Let $M$ be the set of even numbers the permutations act on and $N$ be the set of odd numbers the permutations act on. Then the subgroup in question is
$$S_M\times S_N.$$
Let $M$ be the set of even numbers the permutations act on and $N$ be the set of odd numbers the permutations act on. Then the subgroup in question is
$$S_M\times S_N.$$