Form a list using prime numbers
05AB1E, 13 bytes

Ò.»â€˜ʒ÷DÙQ}θ


Try it online!

A port of my Pyth answer.


Ò gets the prime factÒrs of each.
.» folds a dyadic command, â (cârtesiân product) between each two elements in the list from right to left with opposite right/left operands.
€˜ flattens €ach.
ʒ...} filtʒrs those which satisfy the following condition:


÷ pairwise integer division with the input.
D Duplicate (pushes two copies of the item to the stack).
Ù removes duplicate elements, keeping a ÙniqÙe occurrence of each element.
Q checks for eQuality.

θ gets the last element.