calendar.py

import datetime
from collections import defaultdict
epoch = defaultdict(list)
YEAR = 2013
first_day = datetime.datetime(YEAR, 1, 1)
days_in_year = datetime.datetime(YEAR + 1, 1, 1) - first_day

for denom in range(2, 10) + range(10, 25, 2) + range(25, 51, 5):
    for numer in range(1, denom):
        delta = (days_in_year * numer / denom)
        if delta.seconds:
            days = delta.days
        else:
            days = delta.days - 1

        epoch_day = first_day + datetime.timedelta(days)
        epoch[epoch_day].append('%d/%d' % (numer, denom))

for k in sorted(epoch):
    print k.strftime('%Y-%m-%d'), epoch[k]