644557 has 2 divisors, whose sum is σ = 644558. Its totient is φ = 644556.

The previous prime is 644549. The next prime is 644563. The reversal of 644557 is 755446.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 609961 + 34596 = 781^2 + 186^2 .

It is a cyclic number.

It is not a de Polignac number, because 644557 - 2³ = 644549 is a prime.

It is a Chen prime.

644557 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322278 + 322279.

It is an arithmetic number, because the mean of its divisors is an integer number (322279).

2⁶⁴⁴⁵⁵⁷ is an apocalyptic number.

It is an amenable number.

644557 is a deficient number, since it is larger than the sum of its proper divisors (1).

644557 is an equidigital number, since it uses as much as digits as its factorization.

644557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16800, while the sum is 31.

The square root of 644557 is about 802.8430730846. The cubic root of 644557 is about 86.3814407010.

Subtracting 644557 from its reverse (755446), we obtain a square (110889 = 333²).

The spelling of 644557 in words is "six hundred forty-four thousand, five hundred fifty-seven".