644511820 has 24 divisors (see below), whose sum is σ = 1433091744. Its totient is φ = 242639616.

The previous prime is 644511779. The next prime is 644511827. The reversal of 644511820 is 28115446.

It is a super-2 number, since 2×644511820² = 830790972239424800, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (644511827) 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, 947472 + ... + 948151.

It is an arithmetic number, because the mean of its divisors is an integer number (59712156).

Almost surely, 2^644511820 is an apocalyptic number.

It is an amenable number.

644511820 is an abundant number, since it is smaller than the sum of its proper divisors (788579924).

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

644511820 is a wasteful number, since it uses less digits than its factorization.

644511820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1895649 (or 1895647 counting only the distinct ones).

The product of its (nonzero) digits is 7680, while the sum is 31.

The square root of 644511820 is about 25387.2373447762. The cubic root of 644511820 is about 863.7942236142.

The spelling of 644511820 in words is "six hundred forty-four million, five hundred eleven thousand, eight hundred twenty".