644885881 has 2 divisors, whose sum is σ = 644885882. Its totient is φ = 644885880.

The previous prime is 644885863. The next prime is 644885911. The reversal of 644885881 is 188588446.

644885881 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., 508953600 + 135932281 = 22560^2 + 11659^2 .

It is a cyclic number.

It is not a de Polignac number, because 644885881 - 2¹⁷ = 644754809 is a prime.

It is a super-2 number, since 2×644885881² = 831755599026292322, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (644885981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322442940 + 322442941.

It is an arithmetic number, because the mean of its divisors is an integer number (322442941).

Almost surely, 2^644885881 is an apocalyptic number.

It is an amenable number.

644885881 is a deficient number, since it is larger than the sum of its proper divisors (1).

644885881 is an equidigital number, since it uses as much as digits as its factorization.

644885881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1966080, while the sum is 52.

The square root of 644885881 is about 25394.6033833962. The cubic root of 644885881 is about 863.9613005822.

It can be divided in two parts, 6448 and 85881, that added together give a palindrome (92329).

The spelling of 644885881 in words is "six hundred forty-four million, eight hundred eighty-five thousand, eight hundred eighty-one".