(ttl=n!)

    This indicates that the ttl value in the ICMP "time exceeded"
    packet that we received was unexpected. We expected some initial
    value, for example, the number of routers between our system and
    another system. In other words, if the path from hop 5 to us is
    the same as the path from us to hop 5, we expect to receive a ttl
    value of 4.

    There are several common initial values for ICMP ttls: 255,
    60, 59, 30 and 29. 4.3 tahoe BSD and Cisco routers use 255,
    Proteon routers use either 59 or 29 depending on software
    release, several other implementations use 60 and 30. This
    software uses an initial ttl of 64. The traceroute command
    checks against all of these, making it hard to detect some small
    routing asymmetries. If you want to see the ttl values in all the
    packets, use the -l option.