644640247 has 2 divisors, whose sum is σ = 644640248. Its totient is φ = 644640246.

The previous prime is 644640193. The next prime is 644640259. The reversal of 644640247 is 742046446.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644640247 is a prime.

It is a super-2 number, since 2×644640247² = 831122096104442018, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644640287) 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, 322320123 + 322320124.

It is an arithmetic number, because the mean of its divisors is an integer number (322320124).

Almost surely, 2^644640247 is an apocalyptic number.

644640247 is a deficient number, since it is larger than the sum of its proper divisors (1).

644640247 is an equidigital number, since it uses as much as digits as its factorization.

644640247 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 129024, while the sum is 37.

The square root of 644640247 is about 25389.7665802583. The cubic root of 644640247 is about 863.8515937196.

The spelling of 644640247 in words is "six hundred forty-four million, six hundred forty thousand, two hundred forty-seven".