Let $a_n$ denote the number of permutations of odd order in $S_n$. This is sequence A000246 in OEIS. Then there is the recurrence relation on OEIS that $a_{2n} = (2n-1)a_{2n-1}$ and $a_{2n+1} = (2n+1)a_{2n}$, or equivalently $a_n = a_{n-1} + (n-1)(n-2)a_{n-2}$.
It seems like there should be a combinatorial proof for this result.
Since there isn't a simple recurrence for the number of partitions with odd parts, it doesn't seem like working on the level of partitions will work.
$a_n-a_{n-1}$ is the number of odd order permutations in $S_n$ that move $1$. These permutations look like $(1\, i\,j\,\cdots)\cdots$ where the first cycle has odd length $\ge3$. The number of these is $(n-1)(n-2)t$ where $t$ is the number of odd order permutations $(1\, 2\,3\,\cdots)\cdots$. But these correspond to odd order permutations $(3\,\cdots)\cdots$ of the numbers $3$ to $n$. There are $a_{n-2}$ of these, and this proves your final recurrence.