644565540 has 48 divisors (see below), whose sum is σ = 1910950272. Its totient is φ = 161773056.

The previous prime is 644565499. The next prime is 644565563. The reversal of 644565540 is 45565446.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 314944 + ... + 316983.

It is an arithmetic number, because the mean of its divisors is an integer number (39811464).

Almost surely, 2^644565540 is an apocalyptic number.

644565540 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644565540 is an abundant number, since it is smaller than the sum of its proper divisors (1266384732).

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

644565540 is a wasteful number, since it uses less digits than its factorization.

644565540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 631956 (or 631954 counting only the distinct ones).

The product of its (nonzero) digits is 288000, while the sum is 39.

The square root of 644565540 is about 25388.2953346616. The cubic root of 644565540 is about 863.8182220034.

It can be divided in two parts, 64456 and 5540, that added together give a palindrome (69996).

The spelling of 644565540 in words is "six hundred forty-four million, five hundred sixty-five thousand, five hundred forty".