644881 has 2 divisors, whose sum is σ = 644882. Its totient is φ = 644880.

The previous prime is 644869. The next prime is 644899. The reversal of 644881 is 188446.

644881 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 608400 + 36481 = 780^2 + 191^2 .

It is a cyclic number.

It is not a de Polignac number, because 644881 - 2⁷ = 644753 is a prime.

It is a super-2 number, since 2×644881² = 831743008322, which contains 22 as substring.

644881 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (644801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322440 + 322441.

It is an arithmetic number, because the mean of its divisors is an integer number (322441).

2⁶⁴⁴⁸⁸¹ is an apocalyptic number.

It is an amenable number.

644881 is a deficient number, since it is larger than the sum of its proper divisors (1).

644881 is an equidigital number, since it uses as much as digits as its factorization.

644881 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6144, while the sum is 31.

The square root of 644881 is about 803.0448306290. The cubic root of 644881 is about 86.3959120865.

The spelling of 644881 in words is "six hundred forty-four thousand, eight hundred eighty-one".