644695 has 4 divisors (see below), whose sum is σ = 773640. Its totient is φ = 515752.

The previous prime is 644687. The next prime is 644701. The reversal of 644695 is 596446.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 596446 = 2 ⋅298223.

It is a cyclic number.

It is not a de Polignac number, because 644695 - 2³ = 644687 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644695.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64465 + ... + 64474.

It is an arithmetic number, because the mean of its divisors is an integer number (193410).

2⁶⁴⁴⁶⁹⁵ is an apocalyptic number.

644695 is a deficient number, since it is larger than the sum of its proper divisors (128945).

644695 is a wasteful number, since it uses less digits than its factorization.

644695 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128944.

The product of its digits is 25920, while the sum is 34.

The square root of 644695 is about 802.9290130516. The cubic root of 644695 is about 86.3876050320.

The spelling of 644695 in words is "six hundred forty-four thousand, six hundred ninety-five".