644999 has 2 divisors, whose sum is σ = 645000. Its totient is φ = 644998.

The previous prime is 644977. The next prime is 645011. The reversal of 644999 is 999446.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644999 is a prime.

It is a Chen prime.

It is an Ulam number.

644999 is a modest number, since divided by 999 gives 644 as remainder.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644909) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322499 + 322500.

It is an arithmetic number, because the mean of its divisors is an integer number (322500).

2⁶⁴⁴⁹⁹⁹ is an apocalyptic number.

644999 is a deficient number, since it is larger than the sum of its proper divisors (1).

644999 is an equidigital number, since it uses as much as digits as its factorization.

644999 is an evil number, because the sum of its binary digits is even.

The product of its digits is 69984, while the sum is 41.

The square root of 644999 is about 803.1182976374. The cubic root of 644999 is about 86.4011813253.

The spelling of 644999 in words is "six hundred forty-four thousand, nine hundred ninety-nine".