## Confirmed

Abraham de Moivre correctly predicted the date of his own death.

He noted that he was sleeping 15 minutes longer each day and surmised that he would die on the day he slept for 24 hours. That date, he calculated, would be Nov. 27, 1754.

He was right.

## Burglars Beware

Who says math is too abstract?

The Chvátal Art Gallery Theorem states that if you run an art gallery with *n* corners, you’ll need *n*/3 guards (at most) to watch the entire gallery—regardless of its shape.

## Presto

Pick a three-digit number (example: 412).

Double it to create a six-digit number (412412).

Divide the result successively by 7, by 11, and by 13. There will be no remainders.

The result is the original number.

## “In Event of Moon Disaster”

On July 18, 1969, two days before the first lunar landing, presidential speechwriter William Safire composed the following text to be read by President Nixon if astronauts Neil Armstrong and Edwin Aldrin were stranded on the moon:

Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace.

These brave men, Neil Armstrong and Edwin Aldrin, know that there is no hope for their recovery. But they also know that there is hope for mankind in their sacrifice.

These two men are laying down their lives in mankind’s most noble goal: the search for truth and understanding.

They will be mourned by their families and friends; they will be mourned by the nation; they will be mourned by the people of the world; they will be mourned by a Mother Earth that dared send two of her sons into the unknown.

In their exploration, they stirred the people of the world to feel as one; in their sacrifice, they bind more tightly the brotherhood of man.

In ancient days, men looked at the stars and saw their heroes in the constellations. In modern times, we do much the same, but our heroes are epic men of flesh and blood.

Others will follow, and surely find their way home. Man’s search will not be denied. But these men were the first, and they will remain the foremost in our hearts.

For every human being who looks up at the moon in the nights to come will know that there is some corner of another world that is forever mankind.

Safire also suggested that Nixon call the “widows-to-be” before the speech, and that a clergyman should commend the astronauts’ souls to the “deepest of the deep” when communications ended.

## Proof That 2 Does Not Exist

2 is the only even prime.

But the total number of primes is infinite.

Therefore the probability that a given prime number is even is 1 over infinity, or zero.

Hence it’s impossible for a prime number to be even — and 2 does not exist.

## The Barber’s Dictum

Let’s say that the densest human head of hair contains 200,000 strands, and that the human population is 6 billion. That means there’s a group of at least 30,000 people today who have precisely the same number of hairs on their heads.

Do you see why?

## Waistline

Suppose the earth were a perfect sphere and you fitted a belt around its equator.

The belt would be 40 million meters long. If you now increased its length by a mere 5 meters, how high would it ride above the earth’s surface?

The answer, surprisingly, is 0.8 meters — well above the current limbo record.

## Numerical Pangrams

A pangram is a sentence that uses each letter of the alphabet exactly once:

CWM FJORD BANK GLYPHS VEXT QUIZ.

“Carved symbols in a mountain hollow and on the bank of a fjord irritated an eccentric person.” They’re a bit awkward in English, so here’s the same idea using numbers. Each of these (valid) equations uses the digits 1-9 exactly once:

42 × 138 = 5796

27 × 198 = 5346

39 × 186 = 7254

48 × 159 = 7632

28 × 157 = 4396

4 × 1738 = 6952

4 × 1963 = 7852

Even better: The numbers 3 and 51249876, between them, use all 9 digits — and so does their product, 153749628.

## Torn Up

Imagine a large sheet of rice paper one-thousandth of an inch thick. Tear it in half and stack the pieces, then tear the stack in half and stack those, and so on. If you could do this 50 times in succession, how tall would the final stack be?

A. 0.6 inches

B. 22.84 feet

C. 17 million miles

Surprisingly, the answer is 17 million miles:

2^{50} ply × 0.001 inches/ply

= 1.12589991 × 10^{12} inches

= 17,769,884.9 miles

## Science Fiction

In *Gulliver’s Travels*, Jonathan Swift describes two fictional moons of Mars:

They [the Laputan astronomers] have likewise discovered two lesser stars, or ‘satellites,’ which revolve about Mars, whereof the innermost is distant from the centre of the primary planet exactly three of his diameters, and the outermost five; the former revolves in the space of ten hours, and the latter in twenty-one and a half; so that the squares of their periodical times are very near in the same proportion with the cubes of their distance from the centre of Mars, which evidently shows them to be governed by the same law of gravitation, that influences the other heavenly bodies …

That was in 1726. A century and a half later, two Martian moons were discovered. Phobos and Deimos were in fact about 1.4 and 3.5 diameters from Mars’ center, and they revolved in 7.7 and 30.3 hours, respectively. Voltaire had made a similarly prescient guess in his romance *Micromegas* of 1752.

Fittingly, two craters on Deimos have been named Swift and Voltaire.

## The Life on Mars Paradox

What’s the probability that there are horses on Mars? Let’s be extremely generous and say it’s 1/2. And let’s also say there’s a probability of 1/2 that there are parrots, and aardwolves, and each of 17 other species.

Then the probability that none of these 20 species exists is (1/2)^{20}. And the probability that at least one of them exists is 1 – (1/2)^{20}, or 0.999999046.

Thus it’s nearly certain that there’s life on Mars.