643657 has 4 divisors (see below), whose sum is σ = 735616. Its totient is φ = 551700.

The previous prime is 643651. The next prime is 643661. The reversal of 643657 is 756346.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 643657 - 2³ = 643649 is a prime.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (643651) 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, 45969 + ... + 45982.

It is an arithmetic number, because the mean of its divisors is an integer number (183904).

2⁶⁴³⁶⁵⁷ is an apocalyptic number.

It is an amenable number.

643657 is a deficient number, since it is larger than the sum of its proper divisors (91959).

643657 is an equidigital number, since it uses as much as digits as its factorization.

643657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91958.

The product of its digits is 15120, while the sum is 31.

The square root of 643657 is about 802.2823692441. The cubic root of 643657 is about 86.3412169456.

It can be divided in two parts, 64 and 3657, that added together give a square (3721 = 61²).

The spelling of 643657 in words is "six hundred forty-three thousand, six hundred fifty-seven".