644686447 has 4 divisors (see below), whose sum is σ = 665482816. Its totient is φ = 623890080.

The previous prime is 644686439. The next prime is 644686499. The reversal of 644686447 is 744686446.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 644686447 - 2³ = 644686439 is a prime.

It is a super-2 number, since 2×644686447² = 831241229890967618, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644686447.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644656447) 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, 10398138 + ... + 10398199.

It is an arithmetic number, because the mean of its divisors is an integer number (166370704).

Almost surely, 2^644686447 is an apocalyptic number.

644686447 is a deficient number, since it is larger than the sum of its proper divisors (20796369).

644686447 is a wasteful number, since it uses less digits than its factorization.

644686447 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20796368.

The product of its digits is 3096576, while the sum is 49.

The square root of 644686447 is about 25390.6763793326. The cubic root of 644686447 is about 863.8722300308.

Subtracting 644686447 from its reverse (744686446), we obtain a palindrome (99999999).

The spelling of 644686447 in words is "six hundred forty-four million, six hundred eighty-six thousand, four hundred forty-seven".