I am not sure what the symbol "€" means. If a set has n elements, its powerset has 2ⁿ elements. So, P(S) has 32 elements including the empty set, 5 sets containing 1 element each, 10 elements containing 2 elements each, etc. Make sure you understand what a power set is.

This can be defined as a set of elements of the form 10n + 5 for integer n between 0 and 6.