1573 = 11 x 11 x 13.
1573 is a value of n for which n, 2n, 3n, and 4n all use the same number of digits in Roman numerals.
1573 is a number n for which 10n + 1, 10n + 3, 10n + 7, and 10n + 9 are primes (A007811).
1573 is the sum of the remainders when the 48th prime (223) is divided by primes up to the 47th prime (211) (A033955).
1573 is a concentric tridecagonal number (A195045).
1573 is a divisor of 275 - 1.
1573 has a representation as a sum of two squares: 1573 = 222 + 332.
Source: What's Special About This Number?