def gen_sc3_id(dt, numenc=6, sym="abcdefghijklmnopqrstuvwxyz"):
    """
    Generate an event ID following the SeisComP3 convention. By default it
    divides a year into 26^6 intervals assigning each a unique combination of
    characters.

    >>> from obspy import UTCDateTime
    >>> print(gen_sc3_id(UTCDateTime(2015, 8, 18, 10, 55, 51, 367580)))
    2015qffasl
    """
    numsym = len(sym)
    x = (((((dt.julday - 1) * 24) + dt.hour) * 60 + dt.minute) *
         60 + dt.second) * 1000 + dt.microsecond / 1000
    dx = (((370 * 24) * 60) * 60) * 1000
    rng = numsym ** numenc
    w = int(dx / rng)
    if w == 0:
        w = 1

    if dx >= rng:
        x = int(x / w)
    else:
        x = x * int(rng / dx)
    enc = ''
    for _ in range(numenc):
        r = x % numsym
        enc += sym[r]
        x = int(x / numsym)
    return '%d%s' % (dt.year, enc[::-1])