644621 has 4 divisors (see below), whose sum is σ = 672672. Its totient is φ = 616572.

The previous prime is 644617. The next prime is 644629. The reversal of 644621 is 126446.

It is a happy number.

644621 is nontrivially palindromic in base 7.

644621 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 644621 - 2² = 644617 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23), and also a Moran number because the ratio is a prime number: 28027 = 644621 / (6 + 4 + 4 + 6 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644621.

It is not an unprimeable number, because it can be changed into a prime (644629) 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, 13991 + ... + 14036.

It is an arithmetic number, because the mean of its divisors is an integer number (168168).

2⁶⁴⁴⁶²¹ is an apocalyptic number.

It is an amenable number.

644621 is a deficient number, since it is larger than the sum of its proper divisors (28051).

644621 is a wasteful number, since it uses less digits than its factorization.

644621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28050.

The product of its digits is 1152, while the sum is 23.

The square root of 644621 is about 802.8829304450. The cubic root of 644621 is about 86.3842996306.

The spelling of 644621 in words is "six hundred forty-four thousand, six hundred twenty-one".