It depends on how many letters are in the username and if double letters are allowed.
It is possibly the vowels: A I E O and U
130
There are 130
E, t, a, o, and i.
26 * 5 = 130
A B C D E
The letters j, k, w, x and y are letters that may be described as being in the English, but not the Italian, alphabet. The letters nevertheless do get used since they may be needed for foreign loan words, such as jazz, karaoke, walkie-talkie, xeres and yuppie. Their use introduces five consonants to an alphabet that traditionally preserves five vowels and 21 consonants.
Only one letter of the alphabet starts with t.
It's the same reason that no letters in the English alphabet have a final form: it's just how the writing system evolved.
B,C,D,F, and G
It is possibly the vowels: A I E O and U
120.