C'mon - really?
Surely nobody falls for this? Surely all those people asking "is this true?" are kidding?
I mean, first, Oct 13 is a Monday this year.
Secondly, years repeat their day/date sequence pretty often - 5, 11, 11 years and repeat. So Friday the 13 of any month comes around three times every 27 years (28 for leap years), not 666 years.
But mainly - Halloween is always on Oct 31. Friday the 13th can't possibly come on October 31st.