For prophets of doom, the failure of the world to end Dec. 21 may have been a bit of a letdown. Now, the calendar brings a new possibility for anxious obsession: a whole year ending in the unlucky number 13.

Thirteen has been associated with bad luck for centuries. Many people cite the Biblical Last Supper, where Jesus Christ gathered with his 12 disciples, as a reason for the stigma. In Norse mythology, the troublesome Loki is said to have spoiled a dinner in Valhalla by arriving as the 13th participant. There is even a word for the dread of those digits: triskaidekaphobia.

Ilene Ivins and Brien White plan to marry in October 2013. Brien White

Any year that may begin with a fiscal cliff doesn't sound very promising. Yet, because the past few years have been so distressing, many people figure 2013 can hardly be much worse. "My hope is that things are going to improve," says Suzan Hollist, a substitute teacher in the Pittsburgh area whose son, Parker, was born on a Sept. 13.

Some fretful folks, of course, may have been so fixated on rumors that the world would end on Dec. 21, supposedly the end of the Mayan calendar, that they have only recently begun to stew over the implications of 2013.

There have been some precautions. The Times Square Museum & Visitor Center in New York recently displayed a collection of 13 good-luck charms, including a horseshoe, a four-leaf clover and a rabbit's foot.

America's leading expert on 13 may be Tom Fernsler, a 59-year-old math teacher at the University of Delaware. He became interested in the topic in 1987 when he noticed that there were three Friday the 13ths in that year, something that he later found happens about once every 11 years.

He calculated that there are three Friday the 13ths within six months once every 28 years, as occurred in 2012. Dr. Fernsler, who gives lectures under the name Dr. 13, learned the lore and uses it in programs aimed at making math more fun for children.

When he is asked whether we should be wary of 2013, Dr. Fernsler has no hesitation: "Nah." He believes 13 has become a historic superstition, one people joke about but few fear.

That wasn't the case a century or two ago, according to Nathaniel Lachenmeyer, author of "13," a book published in 2004. Among other superstitions, he wrote, many people believed that if 13 people sat at a table, one would die within a year.

In 1880, Captain William Fowler, a Civil War veteran, tempted fate by creating a club in New York that met on the 13th of each month with 13 members around a dinner table. Menus were printed in the shape of tombstones. Similar clubs arose in other cities. Few if any suspicious deaths ensued. Still, in 1898, the clubhouse of a 13 club in Woodbury, N.J., was blown up with dynamite, injuring three members, Mr. Lachenmeyer found.

There seems to be little historical basis for fearing years ending in 13. As years go, 1913 wasn't particularly calamitous, though it did have its share of untoward events. The 16th amendment created the U.S. federal income tax. A flood devastated Dayton, Ohio. War erupted in the Balkans.

In 1813, Napoleon Bonaparte was on the rampage in Europe. The British burned Buffalo, N.Y. Two centuries before, in 1613, Shakespeare's Globe theater burned down.

Some people saw confirmation of the curse on April 13, 1970, when an explosion aborted the Apollo 13 space mission. That shouldn't have been a surprise. Dr. Fernsler notes that the digits in the launch date—4-11-70—add up to 13 and that the launch pad, 39A, is a multiple of 13.

Even in our supposedly rational age, many hotels lack floors numbered 13. Some airlines do without a row 13.

Most athletes shun No. 13 jerseys. But the basketball star Wilt Chamberlain wore that number on his jersey, as did the football quarterbacks Kurt Warner and Dan Marino. All three are remembered as heroes. That isn't the case for another athlete who wore 13 on his uniform: Ralph Branca, the Brooklyn Dodgers pitcher, today is known almost exclusively for a lapse—the fastball that Bobby Thomson of the New York Giants smacked over the left-field fence of the Polo Grounds to win the 1951 National League pennant.

The fear of similar curses could mean more business for Elaine Ryan, a psychologist in Dublin, Ireland, who helps people cope with anxiety. "I have seen a few people who are genuinely concerned that bad things may happen to them as a direct result of the year being 2013," Ms. Ryan says in an email. She says the fear can cause sweating and heart palpitations—a serious problem because "one year is a long time to live with a stress response."

Sufferers might try breathing techniques, Dr. Ryan suggests: "Start to count your breaths. In one. Out two. In three. Out four. And so on."

One person unlikely to consult Dr. Ryan is the country singer Taylor Swift, whose birthday is Dec. 13. "I love the number 13," she proclaims on her official website. The number is often scrawled on the back of her right hand.

Many others profess to be perfectly calm about prospects for 2013. "The number makes no difference," says Jack Creswell, chairman of Optimist International, the St. Louis-based umbrella group for several thousand Optimist service clubs world-wide. "It's what your target is for yourself as an individual and how that fits into the bigger picture."

Brien White, a graphic artist in Los Angeles, plans to marry Ilene Ivins, a school administrator, next October. Until a reporter asked him about the significance of the year, he says, he and Ms. Ivins had never thought about whether 2013 was propitious for matrimony.

"It's like a nonissue," Ms. Ivins says. Mr. White agrees: "We're not going to let a number deter us from pursuing happiness."

Write to James R. Hagerty at