Wanting to Combine a Shared Prefix and Suffix Onto a Number

I am trying to make a sheet where I can type a set prefix into a designated cell, a set suffix into a designated cell, and have that sandwiched around a list of numbers that will increase by five every time.

For example: prefix is "X" suffix is "Y"

I want it to look like X15Y, X20Y, all the way to X150Y. Preferably descending so I can hit enter to move down a cell.

Thank you!