25
This number is a composite.
25 is a strong pseudoprime base 2 + 5. [Gupta]
The only prime square whose digits are all prime.
The smallest two-digit number N = ab such that the sum and absolute difference
of its digits along with the concatenations of each in both directions are all prime.
E.g., 5 - 2 = 3, 5 + 2 = 7, 37, and 73 are prime. [Heleen]
π(100) = 25.
There are exactly 52 squares less than or equal to 10002 that are the sum of twin prime pairs. [Honaker]
25 is the concatenation of 2 and 5 which are the only primes of the form 10n + 2 and 10n + 5. Note that 25 = 52. [Murthy]
Laura Nickel, a high school student when she made international news by codiscovering the 25th Mersenne prime, is now Ariel Glenn.
There are exactly 25 (a perfect square) primes beginning with the digit 1 among primes smaller than one thousand. It's more than for the other digits. [Capelle]
The smallest composite number whose prime factors are
written with its digits. [Capelle]
25^5+52^2 is a 2+5-digit prime. [Silva]
A prime square whose prime count π(5^2) is another
prime square (3^2) and it's prime count is another prime
square (π(π(5^2)) = 2^2). [Picheny]
The website Prime Rhyme provides 25 words that rhyme with prime.
The only known odd number whose sum of aliquot divisors is
a perfect number. [Gupta]
There are
more than 25 amazing facts about prime numbers.