644661023 has 2 divisors, whose sum is σ = 644661024. Its totient is φ = 644661022.

The previous prime is 644661019. The next prime is 644661037. The reversal of 644661023 is 320166446.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 644661023 - 2² = 644661019 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644661053) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322330511 + 322330512.

It is an arithmetic number, because the mean of its divisors is an integer number (322330512).

Almost surely, 2^644661023 is an apocalyptic number.

644661023 is a deficient number, since it is larger than the sum of its proper divisors (1).

644661023 is an equidigital number, since it uses as much as digits as its factorization.

644661023 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20736, while the sum is 32.

The square root of 644661023 is about 25390.1757181789. The cubic root of 644661023 is about 863.8608739282.

The spelling of 644661023 in words is "six hundred forty-four million, six hundred sixty-one thousand, twenty-three".