644693638 has 8 divisors (see below), whose sum is σ = 967498560. Its totient is φ = 322194120.

The previous prime is 644693633. The next prime is 644693681. The reversal of 644693638 is 836396446.

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

It is a junction number, because it is equal to n+sod(n) for n = 644693591 and 644693600.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644693633) 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, 70998 + ... + 79561.

It is an arithmetic number, because the mean of its divisors is an integer number (120937320).

Almost surely, 2^644693638 is an apocalyptic number.

644693638 is a deficient number, since it is larger than the sum of its proper divisors (322804922).

644693638 is a wasteful number, since it uses less digits than its factorization.

644693638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 152702.

The product of its digits is 2239488, while the sum is 49.

The square root of 644693638 is about 25390.8179860358. The cubic root of 644693638 is about 863.8754419706.

The spelling of 644693638 in words is "six hundred forty-four million, six hundred ninety-three thousand, six hundred thirty-eight".