#1234 - 5678 - 2345 - 3456
16 digits = quadtrillion
million = 1,000,000
billion = 1,000,000,000
trillion = 1,000,000,000,000
quadtrillion = 1,000,000,000,000,000
that means there is only this chance:
of guessing a number that exists.
this is the same as ---
5 out of 100,000,000
or 1 chance in 20,000,000 of fraud