644221407 has 4 divisors (see below), whose sum is σ = 858961880. Its totient is φ = 429480936.

The previous prime is 644221327. The next prime is 644221439. The reversal of 644221407 is 704122446.

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

It is not a de Polignac number, because 644221407 - 2¹⁰ = 644220383 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644221507) 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, 107370232 + ... + 107370237.

It is an arithmetic number, because the mean of its divisors is an integer number (214740470).

Almost surely, 2^644221407 is an apocalyptic number.

644221407 is a deficient number, since it is larger than the sum of its proper divisors (214740473).

644221407 is a wasteful number, since it uses less digits than its factorization.

644221407 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 214740472.

The product of its (nonzero) digits is 10752, while the sum is 30.

The square root of 644221407 is about 25381.5170350395. The cubic root of 644221407 is about 863.6644640289.

The spelling of 644221407 in words is "six hundred forty-four million, two hundred twenty-one thousand, four hundred seven".