643403861 has 2 divisors, whose sum is σ = 643403862. Its totient is φ = 643403860.

The previous prime is 643403833. The next prime is 643403921. The reversal of 643403861 is 168304346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 640393636 + 3010225 = 25306^2 + 1735^2 .

It is a cyclic number.

It is not a de Polignac number, because 643403861 - 2¹⁴ = 643387477 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643403801) 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 as a sum of consecutive naturals, namely, 321701930 + 321701931.

It is an arithmetic number, because the mean of its divisors is an integer number (321701931).

Almost surely, 2^643403861 is an apocalyptic number.

It is an amenable number.

643403861 is a deficient number, since it is larger than the sum of its proper divisors (1).

643403861 is an equidigital number, since it uses as much as digits as its factorization.

643403861 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 41472, while the sum is 35.

The square root of 643403861 is about 25365.4067777357. The cubic root of 643403861 is about 863.2989663310.

The spelling of 643403861 in words is "six hundred forty-three million, four hundred three thousand, eight hundred sixty-one".