644322881 has 4 divisors (see below), whose sum is σ = 644745264. Its totient is φ = 643900500.

The previous prime is 644322869. The next prime is 644322883. The reversal of 644322881 is 188223446.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 188223446 = 2 ⋅94111723.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644322881 is a prime.

It is a super-2 number, since 2×644322881² = 830303949960280322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644322883) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 208895 + ... + 211956.

It is an arithmetic number, because the mean of its divisors is an integer number (161186316).

Almost surely, 2^644322881 is an apocalyptic number.

It is an amenable number.

644322881 is a deficient number, since it is larger than the sum of its proper divisors (422383).

644322881 is a wasteful number, since it uses less digits than its factorization.

644322881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 422382.

The product of its digits is 73728, while the sum is 38.

The square root of 644322881 is about 25383.5159306192. The cubic root of 644322881 is about 863.7098081118.

The spelling of 644322881 in words is "six hundred forty-four million, three hundred twenty-two thousand, eight hundred eighty-one".