53

53 is a prime number. It is also a Sophie Germain prime because 2 x 53 + 1 = 107, which is also a prime.

5 and 3 are the eighth and ninth decimal digits of pi.

53 has a representation as a sum of two squares: 53 = 2² + 7².

53 is the hypotenuse of a primitive Pythagorean triple: 53² = 28² + 45².

53 is the sum of five consecutive primes: 5 + 7 + 11 + 13 + 17 = 53.

The chemical element iodine has atomic number 53.

Source: Prime Curios!