644857 has 2 divisors, whose sum is σ = 644858. Its totient is φ = 644856.

The previous prime is 644843. The next prime is 644863. The reversal of 644857 is 758446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 436921 + 207936 = 661^2 + 456^2 .

It is a cyclic number.

It is not a de Polignac number, because 644857 - 2⁷ = 644729 is a prime.

It is not a weakly prime, because it can be changed into another prime (644837) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322428 + 322429.

It is an arithmetic number, because the mean of its divisors is an integer number (322429).

2⁶⁴⁴⁸⁵⁷ is an apocalyptic number.

It is an amenable number.

644857 is a deficient number, since it is larger than the sum of its proper divisors (1).

644857 is an equidigital number, since it uses as much as digits as its factorization.

644857 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 26880, while the sum is 34.

The square root of 644857 is about 803.0298873641. The cubic root of 644857 is about 86.3948402983.

The spelling of 644857 in words is "six hundred forty-four thousand, eight hundred fifty-seven".