549

549 = 3 x 3 x 61.

549 has a representation as a sum of two squares: 549 = 15² + 18².

549 is 333 in base 13. It is 202100 in base 3 and 20211 in base 4.

The sum of the digits of 549 is six times the number of digits: 5 + 4 + 9 = 6 x 3 = 18.

549 is the number of primes less than 10⁴ having at least one digit 7.

549 is a number n such that n² contains no digit greater than 4: 549² = 301401.

Source: On-Line Encyclopedia of Integer Sequences