644042321 has 8 divisors (see below), whose sum is σ = 693803880. Its totient is φ = 594312192.

The previous prime is 644042299. The next prime is 644042323. The reversal of 644042321 is 123240446.

It can be written as a sum of positive squares in 4 ways, for example, as 16289296 + 627753025 = 4036^2 + 25055^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 644042321 - 2¹⁸ = 643780177 is a prime.

It is a super-2 number, since 2×644042321² = 829581022478134082, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644042323) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 51185 + ... + 62513.

It is an arithmetic number, because the mean of its divisors is an integer number (86725485).

Almost surely, 2^644042321 is an apocalyptic number.

It is an amenable number.

644042321 is a deficient number, since it is larger than the sum of its proper divisors (49761559).

644042321 is a wasteful number, since it uses less digits than its factorization.

644042321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15715.

The product of its (nonzero) digits is 4608, while the sum is 26.

The square root of 644042321 is about 25377.9889077129. The cubic root of 644042321 is about 863.5844270794.

Adding to 644042321 its reverse (123240446), we get a palindrome (767282767).

The spelling of 644042321 in words is "six hundred forty-four million, forty-two thousand, three hundred twenty-one".