643851 has 12 divisors (see below), whose sum is σ = 1001728. Its totient is φ = 396144.

The previous prime is 643849. The next prime is 643859. The reversal of 643851 is 158346.

643851 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 643851 - 2¹ = 643849 is a prime.

It is a super-2 number, since 2×643851² = 829088220402, which contains 22 as substring.

643851 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (643859) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2635 + ... + 2868.

2⁶⁴³⁸⁵¹ is an apocalyptic number.

643851 is a deficient number, since it is larger than the sum of its proper divisors (357877).

643851 is a wasteful number, since it uses less digits than its factorization.

643851 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5522 (or 5519 counting only the distinct ones).

The product of its digits is 2880, while the sum is 27.

The square root of 643851 is about 802.4032651977. The cubic root of 643851 is about 86.3498905681.

The spelling of 643851 in words is "six hundred forty-three thousand, eight hundred fifty-one".