657721 has 3 divisors (see below), whose sum is σ = 658533. Its totient is φ = 656910.

The previous prime is 657719. The next prime is 657743. The reversal of 657721 is 127756.

The square root of 657721 is 811.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 657721 - 2¹ = 657719 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 657721.

It is not an unprimeable number, because it can be changed into a prime (657121) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 406 + ... + 1216.

It is an arithmetic number, because the mean of its divisors is an integer number (219511).

2⁶⁵⁷⁷²¹ is an apocalyptic number.

657721 is the 811-st square number.

657721 is the 406-th centered octagonal number.

It is an amenable number.

657721 is a deficient number, since it is larger than the sum of its proper divisors (812).

657721 is an frugal number, since it uses more digits than its factorization.

657721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1622 (or 811 counting only the distinct ones).

The product of its digits is 2940, while the sum is 28.

The cubic root of 657721 is about 86.9655476392.

It can be divided in two parts, 657 and 721, that added together give a triangular number (1378 = T₅₂).

The spelling of 657721 in words is "six hundred fifty-seven thousand, seven hundred twenty-one".