The smallest number that is the sum of three cubes in two ways:
13 + 53 + 53 = 23 + 33 + 63.
In 1644, Marin Mersenne declared that 2251 - 1 was composite, but gave no proof.
An anonymous seventh grader once said "I noticed that 251, 521, and 2521 - 1 are all prime. Why don't you try 512 * 2512 - 1 or something?"
251 can be expressed using the first three primes: 23 + 35. [Sladcik]
The sum of the letters of "two hundred and fifty one" is the only self-described prime if we use the alphabet code, i.e., a = 1, b = 2, c = 3, etc. [Lundeen]
251 is the only three-digit number such that 2*251^251+1 is prime. [Opao]
The smallest of four consecutive primes in arithmetic progression (251, 257, 263, and 269). [Gallardo]
The Moon not only changes phases from lunation to lunation
but changes in size as the Moon moves closer to and farther
away from the Earth. The length of 18 fumocies is almost
exactly equal to the length of 251 lunations. [Engel]
All the prime numbers up to 251, without repetition, appear
in Benjamin Franklin's original 16-by-16 square. [Capelle]
The only prime n that can be expressed using three
consecutive primes p, q, r so that n = p^q + q^r. [Loungrides]
The sum of the squares of the first three pentatopic numbers (1, 5, 15). [Silva]
Its square is the smallest number n for which the Ramanujan tau-function tau(n) is prime. It was found by D. H. Lehmer in 1965. [Capelle]
Members of the Vermont 251 Club attempt to visit 251 cities and towns in the state of Vermont.
Michael Jackson acquired Sony/ATV Music Publishing which owned the
copyrights to 251 Beatles songs.
2*251^251 + 1 is prime. It is the only known prime with
this property. [Firoozbakht]
To link to this page use http://primes.utm.edu/curios/page.php?number_id=218
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