644401273 has 2 divisors, whose sum is σ = 644401274. Its totient is φ = 644401272.

The previous prime is 644401271. The next prime is 644401279. The reversal of 644401273 is 372104446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 428986944 + 215414329 = 20712^2 + 14677^2 .

It is a cyclic number.

It is not a de Polignac number, because 644401273 - 2¹ = 644401271 is a prime.

Together with 644401271, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (644401271) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322200636 + 322200637.

It is an arithmetic number, because the mean of its divisors is an integer number (322200637).

Almost surely, 2^644401273 is an apocalyptic number.

It is an amenable number.

644401273 is a deficient number, since it is larger than the sum of its proper divisors (1).

644401273 is an equidigital number, since it uses as much as digits as its factorization.

644401273 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16128, while the sum is 31.

The square root of 644401273 is about 25385.0600353830. The cubic root of 644401273 is about 863.7448346467.

The spelling of 644401273 in words is "six hundred forty-four million, four hundred one thousand, two hundred seventy-three".