644561521 has 8 divisors (see below), whose sum is σ = 648909824. Its totient is φ = 640224000.

The previous prime is 644561513. The next prime is 644561539. The reversal of 644561521 is 125165446.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644561521 - 2³ = 644561513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644564521) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 142720 + ... + 147166.

It is an arithmetic number, because the mean of its divisors is an integer number (81113728).

Almost surely, 2^644561521 is an apocalyptic number.

It is an amenable number.

644561521 is a deficient number, since it is larger than the sum of its proper divisors (4348303).

644561521 is a wasteful number, since it uses less digits than its factorization.

644561521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5391.

The product of its digits is 28800, while the sum is 34.

The square root of 644561521 is about 25388.2161838913. The cubic root of 644561521 is about 863.8164266377.

The spelling of 644561521 in words is "six hundred forty-four million, five hundred sixty-one thousand, five hundred twenty-one".