987

987 = 3 x 7 x 47.

987 is the 16th Fibonacci number.

987 is a divisor of 46⁶ - 1.

987 is the only three-digit number with consecutively decreasing digits such that when multiplied by the sum of its digits plus and minus 1, the results are primes: 987(9 + 8 + 7) - 1 = 23,687 and 987(9 + 8 + 7) + 1 = 23,689.

1 x 8 + 1 = 9

12 x 8 + 2 = 98

123 x 8 + 3 = 987

1234 x 8 + 4 = 9876

12345 x 8 + 5 = 98765

987 Hotels has hotels in Prague and Barcelona.

Source: Prime Curios!

377

377 = 13 x 29.

377 has two representations as a sum of two squares: 377 = 4² + 19² = 11² + 16².

377 is the fourteenth Fibonacci number. It is the largest known Fibonacci number whose digits are all prime.

377 is the hypotenuse of two primitive Pythagorean triples: 377² = 135² + 352² = 152² + 345².

377 is the sum of the squares of the first six primes: 377 = 2² + 3² + 5² + 7² + 11² + 13².

The Aero Spacelines B-377 SG Super Guppy is a four-engine oversize-cargo freighter aircraft.

Source: Prime Curios!

21

21 = 3 x 7.

21 is 10101 in base 2 (binary) and 111 in base 4.

21 has a unique representation as a sum of three squares: 21 = 1² + 2² + 4².

21 is the smallest number with five representations as a sum of three primes: 21 = 2 + 2 + 17 = 3 + 5 + 13 = 3 + 7 + 11 = 5 + 5 + 11 = 7 + 7 + 7.

21 is the eighth Fibonacci number.

21 is the fifth Motzkin number.

21 is the sixth triangular number.

21 is the total number of spots on a normal die.

Source: Phillips, R. 2004. Numbers: Facts, Figures and Fiction. Badsey Publications.

55

55 = 5 x 11.

55 is the tenth Fibonacci number.

55 is the tenth triangular number.

55 is a pyramidal number, the sum of the first five square numbers: 55 = 1² + 2² + 3² + 4² + 5².

55 is a number that cannot be written as a sum of three squares.

An emerald anniversary celebrates 55 years.

Source: Phillips, R. 2004. Numbers: Facts, Figures and Fiction. Badsey Publications.

144

144 = 2⁴ x 3².

144² = 12², a perfect square. If you reverse the digits, 21² = 441.

144 has a unique representation as a sum of three squares: 144 = 4² + 8² + 8².

144 is a square number. Divide it by 4 and you get 36, which is also square. Does this happen with any other square numbers?

144 is the 12th Fibonacci number.

144 is 99 in base 15.

The interior angles in a regular decagon measure 144 degrees. In counting objects, 144 is called a gross (a dozen dozens).

Source: WolframAlpha

89

89 is a prime number.

89 is the smallest prime whose digits, 8 and 9, are composites.

89 is the eleventh Fibonacci number.

89 is the only two-digit number that is the sum of its first digit and its second digit squared: 8 + 9² = 89.

A sunflower head often displays florets in spirals of 55 and 89 around the outside.

Source: Number Gossip

34

34 = 2 x 17.

34 is the ninth Fibonacci number.

34 is the smallest number with the property that it and its neighbors have the same number of divisors (four): 33 = 3 x 11; 34 = 2 x 17; 35 = 5 x 7.

The rows and columns of a 4 x 4 magic square always total 34.

34 has a representation as a sum of two squares: 34 = 3² + 5².

34 is the smallest number with four representations as a sum of two primes: 34 = 3 + 31 = 5 + 29 = 11 + 23 = 17 + 17.

34 is 22 in base 16.

34 is a heptagonal number.


34 is the atomic number of the element selenium.

Source: Number Gossip

233

233 is a prime number. It is a Sophie Germain prime because 2 x 233 + 1 = 467 is also a prime.

233 is the 13th Fibonacci number.

233 is the only known Fibonacci prime whose sum of digits is a Fibonacci number: 2 + 3 + 3 = 8.

233 has a representation as a sum of two squares: 233 = 8² + 13².

233 is the smallest number with the property that it and its neighbors can be written as a sum of two squares and therefore can be the hypotenuse of a Pythagorean triangle: 233² = 105² + 208².

2²³³ - 3 is a prime.


Had Ray Bradbury used the metric system, he may have called his novel Celsius 233 instead of Fahrenheit 451.

Source: Number Gossip