643990181 has 2 divisors, whose sum is σ = 643990182. Its totient is φ = 643990180.

The previous prime is 643990177. The next prime is 643990189. The reversal of 643990181 is 181099346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 468029956 + 175960225 = 21634^2 + 13265^2 .

It is a cyclic number.

It is not a de Polignac number, because 643990181 - 2² = 643990177 is a prime.

It is a super-3 number, since 3×643990181³ (a number of 27 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643990189) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321995090 + 321995091.

It is an arithmetic number, because the mean of its divisors is an integer number (321995091).

Almost surely, 2^643990181 is an apocalyptic number.

It is an amenable number.

643990181 is a deficient number, since it is larger than the sum of its proper divisors (1).

643990181 is an equidigital number, since it uses as much as digits as its factorization.

643990181 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 46656, while the sum is 41.

The square root of 643990181 is about 25376.9616187596. The cubic root of 643990181 is about 863.5611219302.

The spelling of 643990181 in words is "six hundred forty-three million, nine hundred ninety thousand, one hundred eighty-one".