644638849 has 4 divisors (see below), whose sum is σ = 645038640. Its totient is φ = 644239060.

The previous prime is 644638847. The next prime is 644638853. The reversal of 644638849 is 948836446.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 644638849 - 2¹ = 644638847 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 644638796 and 644638805.

It is not an unprimeable number, because it can be changed into a prime (644638847) 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, 197467 + ... + 200704.

It is an arithmetic number, because the mean of its divisors is an integer number (161259660).

Almost surely, 2^644638849 is an apocalyptic number.

It is an amenable number.

644638849 is a deficient number, since it is larger than the sum of its proper divisors (399791).

644638849 is a wasteful number, since it uses less digits than its factorization.

644638849 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 399790.

The product of its digits is 3981312, while the sum is 52.

The square root of 644638849 is about 25389.7390494664. The cubic root of 644638849 is about 863.8509692548.

The spelling of 644638849 in words is "six hundred forty-four million, six hundred thirty-eight thousand, eight hundred forty-nine".