644742621 has 24 divisors (see below), whose sum is σ = 945152000. Its totient is φ = 423457632.

The previous prime is 644742613. The next prime is 644742661. The reversal of 644742621 is 126247446.

644742621 is a `hidden beast` number, since 644 + 7 + 4 + 2 + 6 + 2 + 1 = 666.

It is not a de Polignac number, because 644742621 - 2³ = 644742613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644742661) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 503460 + ... + 504738.

Almost surely, 2^644742621 is an apocalyptic number.

It is an amenable number.

644742621 is a deficient number, since it is larger than the sum of its proper divisors (300409379).

644742621 is a wasteful number, since it uses less digits than its factorization.

644742621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2073 (or 2070 counting only the distinct ones).

The product of its digits is 64512, while the sum is 36.

The square root of 644742621 is about 25391.7825486908. The cubic root of 644742621 is about 863.8973201344.

The spelling of 644742621 in words is "six hundred forty-four million, seven hundred forty-two thousand, six hundred twenty-one".