644869 has 2 divisors, whose sum is σ = 644870. Its totient is φ = 644868.

The previous prime is 644867. The next prime is 644881. The reversal of 644869 is 968446.

644869 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 562500 + 82369 = 750^2 + 287^2 .

It is a cyclic number.

It is not a de Polignac number, because 644869 - 2¹ = 644867 is a prime.

It is a super-2 number, since 2×644869² = 831712054322, which contains 22 as substring.

Together with 644867, it forms a pair of twin primes.

644869 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322434 + 322435.

It is an arithmetic number, because the mean of its divisors is an integer number (322435).

2⁶⁴⁴⁸⁶⁹ is an apocalyptic number.

It is an amenable number.

644869 is a deficient number, since it is larger than the sum of its proper divisors (1).

644869 is an equidigital number, since it uses as much as digits as its factorization.

644869 is an evil number, because the sum of its binary digits is even.

The product of its digits is 41472, while the sum is 37.

The square root of 644869 is about 803.0373590313. The cubic root of 644869 is about 86.3953761957.

The spelling of 644869 in words is "six hundred forty-four thousand, eight hundred sixty-nine".