644291969 has 2 divisors, whose sum is σ = 644291970. Its totient is φ = 644291968.

The previous prime is 644291951. The next prime is 644291971. The reversal of 644291969 is 969192446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 365001025 + 279290944 = 19105^2 + 16712^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644291969 is a prime.

It is a super-2 number, since 2×644291969² = 830224282635793922, which contains 22 as substring.

Together with 644291971, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644291909) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322145984 + 322145985.

It is an arithmetic number, because the mean of its divisors is an integer number (322145985).

Almost surely, 2^644291969 is an apocalyptic number.

It is an amenable number.

644291969 is a deficient number, since it is larger than the sum of its proper divisors (1).

644291969 is an equidigital number, since it uses as much as digits as its factorization.

644291969 is an evil number, because the sum of its binary digits is even.

The product of its digits is 839808, while the sum is 50.

The square root of 644291969 is about 25382.9070242161. The cubic root of 644291969 is about 863.6959954591.

The spelling of 644291969 in words is "six hundred forty-four million, two hundred ninety-one thousand, nine hundred sixty-nine".