644439923 has 2 divisors, whose sum is σ = 644439924. Its totient is φ = 644439922.

The previous prime is 644439911. The next prime is 644439973. The reversal of 644439923 is 329934446.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 644439923 - 2²⁰ = 643391347 is a prime.

It is not a weakly prime, because it can be changed into another prime (644439973) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322219961 + 322219962.

It is an arithmetic number, because the mean of its divisors is an integer number (322219962).

Almost surely, 2^644439923 is an apocalyptic number.

644439923 is a deficient number, since it is larger than the sum of its proper divisors (1).

644439923 is an equidigital number, since it uses as much as digits as its factorization.

644439923 is an evil number, because the sum of its binary digits is even.

The product of its digits is 559872, while the sum is 44.

The square root of 644439923 is about 25385.8212985123. The cubic root of 644439923 is about 863.7621029089.

The spelling of 644439923 in words is "six hundred forty-four million, four hundred thirty-nine thousand, nine hundred twenty-three".