643979 has 4 divisors (see below), whose sum is σ = 735984. Its totient is φ = 551976.

The previous prime is 643969. The next prime is 643991. The reversal of 643979 is 979346.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 979346 = 2 ⋅489673.

It is a cyclic number.

It is not a de Polignac number, because 643979 - 2⁸ = 643723 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (643919) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 45992 + ... + 46005.

It is an arithmetic number, because the mean of its divisors is an integer number (183996).

2⁶⁴³⁹⁷⁹ is an apocalyptic number.

643979 is a deficient number, since it is larger than the sum of its proper divisors (92005).

643979 is an equidigital number, since it uses as much as digits as its factorization.

643979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92004.

The product of its digits is 40824, while the sum is 38.

The square root of 643979 is about 802.4830216272. The cubic root of 643979 is about 86.3556124166.

The spelling of 643979 in words is "six hundred forty-three thousand, nine hundred seventy-nine".