Answer: The day is doubly worrisome in that both Fridays and the number 13 have been believed unlucky. Fear of 13 goes by the seemingly unpronounceable "triskaidekaphobia," from the Greek "tris" for three, "kai" for and, "deka" for 10, plus "phobia" for fear, says Julian Havil in "Nonplussed! Mathematical Proof of Implausible Ideas."

Fretting over the number 13 has any number of justifications: 13 were present at the Last Supper; in Norse mythology there were 13 at a banquet when the son of Odin was slain, leading to the downfall of the gods; the near-catastrophic explosion on the moon rocket "Apollo 13" on 13 April 1970, two days after its launch at 13:13:00 CST from pad 39 (13 x 3).

And as unluck would have it, every year has at least one Friday the 13th and many have three, in February, March and November for a non-leap year; January, April and July for a leap year. As you can see, the only possibility for consecutive months having Friday the 13th is February and March of a non-leap year. For you triskaidekaphobes, the next consecutives are in 2009, 2015 and 2026.