644947181 has 2 divisors, whose sum is σ = 644947182. Its totient is φ = 644947180.

The previous prime is 644947141. The next prime is 644947183. The reversal of 644947181 is 181749446.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 426794281 + 218152900 = 20659^2 + 14770^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644947181 is a prime.

It is a super-2 number, since 2×644947181² = 831913732559693522, which contains 22 as substring.

Together with 644947183, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644947183) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322473590 + 322473591.

It is an arithmetic number, because the mean of its divisors is an integer number (322473591).

Almost surely, 2^644947181 is an apocalyptic number.

It is an amenable number.

644947181 is a deficient number, since it is larger than the sum of its proper divisors (1).

644947181 is an equidigital number, since it uses as much as digits as its factorization.

644947181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 193536, while the sum is 44.

The square root of 644947181 is about 25395.8103040639. The cubic root of 644947181 is about 863.9886744950.

The spelling of 644947181 in words is "six hundred forty-four million, nine hundred forty-seven thousand, one hundred eighty-one".