643985 has 12 divisors (see below), whose sum is σ = 807348. Its totient is φ = 492768.

The previous prime is 643969. The next prime is 643991. The reversal of 643985 is 589346.

643985 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 2 ways, for example, as 421201 + 222784 = 649^2 + 472^2 .

It is not a de Polignac number, because 643985 - 2⁴ = 643969 is a prime.

It is an Ulam number.

It is a Duffinian number.

Its product of digits (25920) is a multiple of the sum of its prime factors (160).

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10886 + ... + 10944.

It is an arithmetic number, because the mean of its divisors is an integer number (67279).

2⁶⁴³⁹⁸⁵ is an apocalyptic number.

It is an amenable number.

643985 is a deficient number, since it is larger than the sum of its proper divisors (163363).

643985 is an equidigital number, since it uses as much as digits as its factorization.

643985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 160 (or 101 counting only the distinct ones).

The product of its digits is 25920, while the sum is 35.

The square root of 643985 is about 802.4867600154. The cubic root of 643985 is about 86.3558806097.

The spelling of 643985 in words is "six hundred forty-three thousand, nine hundred eighty-five".