644961 has 4 divisors (see below), whose sum is σ = 859952. Its totient is φ = 429972.

The previous prime is 644951. The next prime is 644977. The reversal of 644961 is 169446.

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 not a de Polignac number, because 644961 - 2¹⁵ = 612193 is a prime.

It is a D-number.

It is a Duffinian number.

644961 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (644911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107491 + ... + 107496.

It is an arithmetic number, because the mean of its divisors is an integer number (214988).

2⁶⁴⁴⁹⁶¹ is an apocalyptic number.

It is an amenable number.

644961 is a deficient number, since it is larger than the sum of its proper divisors (214991).

644961 is a wasteful number, since it uses less digits than its factorization.

644961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214990.

The product of its digits is 5184, while the sum is 30.

The square root of 644961 is about 803.0946395040. The cubic root of 644961 is about 86.3994845220.

The spelling of 644961 in words is "six hundred forty-four thousand, nine hundred sixty-one".