643811861 has 16 divisors (see below), whose sum is σ = 830355840. Its totient is φ = 484370880.

The previous prime is 643811821. The next prime is 643811897. The reversal of 643811861 is 168118346.

It is not a de Polignac number, because 643811861 - 2¹⁸ = 643549717 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (643811821) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 141926 + ... + 146391.

It is an arithmetic number, because the mean of its divisors is an integer number (51897240).

Almost surely, 2^643811861 is an apocalyptic number.

It is an amenable number.

643811861 is a deficient number, since it is larger than the sum of its proper divisors (186543979).

643811861 is a wasteful number, since it uses less digits than its factorization.

643811861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 288364.

The product of its digits is 27648, while the sum is 38.

The square root of 643811861 is about 25373.4479525349. The cubic root of 643811861 is about 863.4814082745.

The spelling of 643811861 in words is "six hundred forty-three million, eight hundred eleven thousand, eight hundred sixty-one".