644740247 has 2 divisors, whose sum is σ = 644740248. Its totient is φ = 644740246.

The previous prime is 644740199. The next prime is 644740289. The reversal of 644740247 is 742047446.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 644740247 - 2¹² = 644736151 is a prime.

It is a super-2 number, since 2×644740247² = 831379972203242018, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 644740247.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644340247) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322370123 + 322370124.

It is an arithmetic number, because the mean of its divisors is an integer number (322370124).

Almost surely, 2^644740247 is an apocalyptic number.

644740247 is a deficient number, since it is larger than the sum of its proper divisors (1).

644740247 is an equidigital number, since it uses as much as digits as its factorization.

644740247 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 150528, while the sum is 38.

The square root of 644740247 is about 25391.7358012405. The cubic root of 644740247 is about 863.8962598174.

The spelling of 644740247 in words is "six hundred forty-four million, seven hundred forty thousand, two hundred forty-seven".