644377521 has 4 divisors (see below), whose sum is σ = 859170032. Its totient is φ = 429585012.

The previous prime is 644377519. The next prime is 644377523. The reversal of 644377521 is 125773446.

644377521 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 an interprime number because it is at equal distance from previous prime (644377519) and next prime (644377523).

It is not a de Polignac number, because 644377521 - 2¹ = 644377519 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 644377521.

It is not an unprimeable number, because it can be changed into a prime (644377523) 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, 107396251 + ... + 107396256.

It is an arithmetic number, because the mean of its divisors is an integer number (214792508).

Almost surely, 2^644377521 is an apocalyptic number.

It is an amenable number.

644377521 is a deficient number, since it is larger than the sum of its proper divisors (214792511).

644377521 is a wasteful number, since it uses less digits than its factorization.

644377521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214792510.

The product of its digits is 141120, while the sum is 39.

The square root of 644377521 is about 25384.5921968426. The cubic root of 644377521 is about 863.7342222533.

The spelling of 644377521 in words is "six hundred forty-four million, three hundred seventy-seven thousand, five hundred twenty-one".