644540520 has 64 divisors (see below), whose sum is σ = 2082366720. Its totient is φ = 158655744.

The previous prime is 644540509. The next prime is 644540527. The reversal of 644540520 is 25045446.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (644540527) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 205024 + ... + 208143.

It is an arithmetic number, because the mean of its divisors is an integer number (32536980).

Almost surely, 2^644540520 is an apocalyptic number.

644540520 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644540520 is an abundant number, since it is smaller than the sum of its proper divisors (1437826200).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644540520 is a wasteful number, since it uses less digits than its factorization.

644540520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 413194 (or 413190 counting only the distinct ones).

The product of its (nonzero) digits is 19200, while the sum is 30.

The square root of 644540520 is about 25387.8025831303. The cubic root of 644540520 is about 863.8070449597.

Adding to 644540520 its reverse (25045446), we get a palindrome (669585966).

The spelling of 644540520 in words is "six hundred forty-four million, five hundred forty thousand, five hundred twenty".