Another Friday the 13th is upon us. For people like Thomas Fernsler, PhD, this is a day he relishes. For other, though, the thought of friday the 13th is enough to send them under the cover until... Well, at least the 14th. Tridkaidekaphobia,fear of the number 13, is a source of fascination to Fernsler,who - at least in the world of mathematics - has become known as "Dr.13.