The way you run your cronjob (without
> /dev/null 2>&1) suggests that the actual output from your cronjob should be in your user's mailbox.
Check your mail on the server.
(as an aside, I don't think
*/13 notation transcends boundaries, so it will run at 0, 13, 26, 39, 42, 55, 0, 13, ..., etc, minutes past the hour, but I may be wrong
)