644972618 has 8 divisors (see below), whose sum is σ = 967695012. Its totient is φ = 322407616.

The previous prime is 644972569. The next prime is 644972633. The reversal of 644972618 is 816279446.

It can be written as a sum of positive squares in 2 ways, for example, as 430438009 + 214534609 = 20747^2 + 14647^2 .

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

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 28505 + ... + 45852.

Almost surely, 2^644972618 is an apocalyptic number.

644972618 is a deficient number, since it is larger than the sum of its proper divisors (322722394).

644972618 is a wasteful number, since it uses less digits than its factorization.

644972618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78696.

The product of its digits is 580608, while the sum is 47.

The square root of 644972618 is about 25396.3111100805. The cubic root of 644972618 is about 864.0000330433. Note that the first 4 decimals are identical.

The spelling of 644972618 in words is "six hundred forty-four million, nine hundred seventy-two thousand, six hundred eighteen".