644702321 has 2 divisors, whose sum is σ = 644702322. Its totient is φ = 644702320.

The previous prime is 644702287. The next prime is 644702323. The reversal of 644702321 is 123207446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 404452321 + 240250000 = 20111^2 + 15500^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644702321 is a prime.

Together with 644702323, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644702323) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322351160 + 322351161.

It is an arithmetic number, because the mean of its divisors is an integer number (322351161).

Almost surely, 2^644702321 is an apocalyptic number.

It is an amenable number.

644702321 is a deficient number, since it is larger than the sum of its proper divisors (1).

644702321 is an equidigital number, since it uses as much as digits as its factorization.

644702321 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8064, while the sum is 29.

The square root of 644702321 is about 25390.9889724682. The cubic root of 644702321 is about 863.8793202968.

Adding to 644702321 its reverse (123207446), we get a palindrome (767909767).

The spelling of 644702321 in words is "six hundred forty-four million, seven hundred two thousand, three hundred twenty-one".