Palindromic rearrangements of MISSISSIPPI

Consider all distinct rearrangements of the eleven letters in MISSISSIPPI. How many of them read identically left to right and right to left?

$30$. With 11 letters and only one M, the M must sit in the middle. Each half then needs two S's, two I's and one P, and choosing the left half fixes the right. The left half can be arranged in $\tfrac{5!}{2!\,2!\,1!}=30$ ways.