263 is a prime number.
263 is the largest known prime whose square is strobogrammatic; that is, it is the same number when rotated 180 degrees: 2632 = 69169.
263 is the smallest prime number that is the sum of primes beginning and ending with the digit 1: 263 = 11 + 101 + 151. Note that the digit sum of each prime is prime and that the digit sum of 263 is a prime and begins and ends with the digit 1.
263 is the only prime with three distinct digits, where one is the product of the other two.
263 is the smallest prime formed be inserting a semiprime, 6, between the semiprime's factors, 2 and 3.
263 is a number that cannot be written as a sum of three squares.
Anne Frank (and her family) hid from the Nazis in an annex behind the house at 263 Prinsengracht 263 in Amsterdam.
Source: Prime Curios!