643866809 has 2 divisors, whose sum is σ = 643866810. Its totient is φ = 643866808.

The previous prime is 643866793. The next prime is 643866871. The reversal of 643866809 is 908668346.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 485232784 + 158634025 = 22028^2 + 12595^2 .

It is a cyclic number.

It is not a de Polignac number, because 643866809 - 2⁴ = 643866793 is a prime.

It is not a weakly prime, because it can be changed into another prime (643866409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321933404 + 321933405.

It is an arithmetic number, because the mean of its divisors is an integer number (321933405).

Almost surely, 2^643866809 is an apocalyptic number.

It is an amenable number.

643866809 is a deficient number, since it is larger than the sum of its proper divisors (1).

643866809 is an equidigital number, since it uses as much as digits as its factorization.

643866809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1492992, while the sum is 50.

The square root of 643866809 is about 25374.5307148723. The cubic root of 643866809 is about 863.5059730216.

The spelling of 643866809 in words is "six hundred forty-three million, eight hundred sixty-six thousand, eight hundred nine".