There's a devilishly odd nexus of theology, mathematics and commercialism on the sixth day of the sixth month of the sixth year. OK, it's just the sixth year of this millennium, but insisting on calling it 2006 takes the devil-may-care fun out of calendar-gazing.

Something about the number 666 brings out the worry, the hope and even the humor in people, said the Rev. Felix Just, a professor of theology at the University of San Francisco. A Jesuit priest, Just has taught both apocalyptic theory and mathematics and maintains a "666-Numbers of the Beast" Web site that contains history, theology, math and precisely 66 one-line jokes about 666.

You can even make sport of it, betting online whether the apocalypse will happen on that date. The good news is that one online oddsmaker has made the world a 100,000-to-1 favorite to survive Tuesday ¡ª something that Just said is supported by theology.

"Many people avoid the number; they're afraid of it almost and there's absolutely no reason to be afraid of it," Just said. "It is not a prediction of future events. It is not supposed to be taken as a timetable for when the world is going to end."

It all started with Revelation 13:18 in the Bible: "This calls for wisdom: let him who has understanding reckon the number of the beast, for it is a human number, its number is six hundred and sixty-six."

The beast is also known as the Antichrist, according to some apocalyptic theories.

Many scholars, such as Just, say the beast is really a coded reference ¡ª using Hebrew letters for numbers ¡ª for the despotic Roman emperor Nero and 616 appears instead of 666 in some ancient manuscripts. The Book of Revelation isn't prophesying a specific end of times but "is about the overall cosmic struggle of good versus evil," Just said.

But for some more apocalyptic theologians, the end of times is coming, even if not specifically on Tuesday. The evangelical Raptureready.com Web site puts its "rapture index" at 156, calling that "fasten your seatbelts" time.

It's not the date June 6 that's worrisome, but the signs in our society of the approach of the 666 antichrist, said the Rev. Tim LaHaye, founder of a self-named ministry and co-author of the best-selling "Left Behind" series of apocalyptic novels. And even though LaHaye said Tuesday isn't the date of the apocalypse, his Left Behind Web site promotes his new book "The Rapture" with an ominous "06.06.06 Will You Be Ready."

"I don't think that people understand that 666 is not a good time," LaHaye said. He said he sees signs of an upcoming "tribulation period" that leads to the Antichrist's arrival in a movement toward one-world government, a single economic system and single religion.

Apocalyptic culture and theology, especially those surrounding 666, "is especially appealing for people in an underdog situation," said Just (pronounced Yoost).

So people have looked for ¡ª and found ¡ª 666 in all sorts of places. Believers in the number's power have used biblical letter-numeric code to convert the names of countless political leaders, including many popes, to come out 666, marking them as that generation's Antichrist. That includes Franklin Delano Roosevelt, John F. Kennedy, Ronald Reagan and Bill Clinton.

It's a number that the Reagans didn't want as an address when they moved out of the White House in 1989 to the Los Angeles neighborhood of Bel-Air. So they changed their address from 666 St. Cloud Road to 668. In 1980, a TV host and others rigged the number 666 to come up in a Pennsylvania lottery drawing. It's a number that is part of every UPC barcode on groceries (a coincidence according to the code's inventor). With biblical coding, 666 also is the number for the WWW of the World Wide Web.

The math of 666 is also open to biblical interpretation and manipulation. Just points out that 666 is the sum of all the numbers on a roulette wheel. Other oddities include variations on pi and products of prime number multiplication.

There's also something special about the number 6, which in the Bible stands for man, said Brian C. Jones, a religion professor at Wartburg College in Iowa.

"People need to lighten up about this," Jones said, adding that it's hard to take a Tuesday seriously as a day of reckoning. "Monday, we always hate Mondays. Wednesday is hump day. Friday sometimes has the 13th attached to it. But Tuesdays and Thursdays, they don't ring for me as days when bad things happen or good things happen. They're filler days."

But it's a day to cash in on the number associated with the apocalypse. Tuesday will mark the debut for a remake of the classic 1970s horror film "The Omen," the publication of LaHaye's new "Left Behind" book, and an Ann Coulter polemic called "Godless: The Church of Liberalism."

And for truly cashing in, there's the nonsectarian online sports book, BetUS.com, which gives Earth a better than sporting chance. At 100,000-to-1 odds, if you bet the maximum $500 that the world will survive and it does, you win half a penny. If you bet $100 that the apocalypse happens and it does, you can earn a cool $10 million, but you might have a devil of a time collecting it. People are betting both ways, company spokesman Mike Foreman said.

Commercialism based on numbers and fear bothers American University astronomer Richard Berendzen.

"What it really does is use some coincidence of some numbers for commercial gain," he said. "It's superstition and money when it comes down to it. And that's about as satanic as you can get."

Still scared about the date 666? Jack Horkheimer of the Miami Space Transit Planetarium has a piece of advice: "If it really spooks you, you can stand on your head and it'll be 999."