657991 has 4 divisors (see below), whose sum is σ = 666400. Its totient is φ = 649584.

The previous prime is 657983. The next prime is 658001. The reversal of 657991 is 199756.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 657991 - 2³ = 657983 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 657991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (657911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4086 + ... + 4243.

It is an arithmetic number, because the mean of its divisors is an integer number (166600).

2⁶⁵⁷⁹⁹¹ is an apocalyptic number.

657991 is a deficient number, since it is larger than the sum of its proper divisors (8409).

657991 is an equidigital number, since it uses as much as digits as its factorization.

657991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8408.

The product of its digits is 17010, while the sum is 37.

The square root of 657991 is about 811.1664440791. The cubic root of 657991 is about 86.9774460407.

It can be divided in two parts, 6579 and 91, that added together give a triangular number (6670 = T₁₁₅).

The spelling of 657991 in words is "six hundred fifty-seven thousand, nine hundred ninety-one".