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import calendar
from itertools import product

def is_jason_spawn(year, month):
for week in calendar.monthcalendar(year, month):
if 13 in week and week.index(13) == 4:
return True
return False

for year,month in product(range(2018, 2050), range(1, 12)):
if is_jason_spawn(year, month):
print(year, month)

どうやらほぼ毎年一度は来てくれるようだ。少なくとも2049年までは。