571

571 is the natural number that follows 570 and precedes 572. It is a prime number, specifically the 105th prime. It is odd and congruent to 3 modulo 4, which means it cannot be expressed as a sum of two squares. The sum of its divisors is 1 + 571 = 572, so 571 is a deficient number.

In various base representations, 571 appears as 1000111011 in binary and 0x23B in hexadecimal. In Roman numerals it is written as DLXXI. It also has a notable position in figurate numbers: 571 is the 20th centered triangular number, generated by the formula 3n(n−1)/2 + 1 with n = 20, yielding 571.

571 has uses beyond pure mathematics. It is the area code 571 for Northern Virginia, introduced as an overlay for 703 in 2000. In calendar contexts, 571 can denote a year in the common era (571 CE) or, in historical dating, a year in the previous era as a BCE value.