5555

5555 is a natural number that consists of four identical digits, making it a repdigit and a palindrome in decimal notation. It sits between 5554 and 5556.

In terms of basic properties, 5555 is odd and divisible by 5. Its prime factorization is 5 × 11 × 101, meaning it is the product of three distinct primes and is therefore square-free. It can also be expressed as 55 × 101 or 5 × 1111. The digit sum of 5555 is 20, so it is not divisible by 3, and its digital root is 2. In binary, 5555 is represented as 1010110110011.

As a four-digit repdigit, 5555 is often cited as an example in discussions of factorization and divisibility rules. The divisibility by 11 can be demonstrated using the standard test: for 5555, the alternating-sum difference is (5 + 5) − (5 + 5) = 0, which confirms divisibility by 11.

Culturally, sequences such as 555 are widely used in media to denote fictional phone numbers, but 5555 itself is primarily encountered as a numeric label or mathematical example rather than a specific identifier with broader usage. See also: repdigit, 555, integer factorization.