644252261 has 4 divisors (see below), whose sum is σ = 665034624. Its totient is φ = 623469900.

The previous prime is 644252249. The next prime is 644252269. The reversal of 644252261 is 162252446.

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.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644252261 is a prime.

It is a super-2 number, since 2×644252261² = 830121951607224242, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644252269) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10391135 + ... + 10391196.

It is an arithmetic number, because the mean of its divisors is an integer number (166258656).

Almost surely, 2^644252261 is an apocalyptic number.

It is an amenable number.

644252261 is a deficient number, since it is larger than the sum of its proper divisors (20782363).

644252261 is a wasteful number, since it uses less digits than its factorization.

644252261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20782362.

The product of its digits is 23040, while the sum is 32.

The square root of 644252261 is about 25382.1248322515. The cubic root of 644252261 is about 863.6782517721.

The spelling of 644252261 in words is "six hundred forty-four million, two hundred fifty-two thousand, two hundred sixty-one".