You have 5 choices for each character. If you have limit to 5 character words you can assume that all 5 char, 4 char, 3, 2, 1 and 0 char words are included too.

I get:

    5^0+5^1+5^2+5^3+5^4+5^5 = 3,906

But I may have totally missed something.

Edit: looking a little closer I see some italics in your 55555 so I guess you have 5 * 5 * 5 * 5 * 5