21679939 has 4 divisors (see below), whose sum is σ = 22208760. Its totient is φ = 21151120.

The previous prime is 21679909. The next prime is 21679967. The reversal of 21679939 is 93997612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21679939 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21679909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 264349 + ... + 264430.

It is an arithmetic number, because the mean of its divisors is an integer number (5552190).

Almost surely, 2^21679939 is an apocalyptic number.

21679939 is a deficient number, since it is larger than the sum of its proper divisors (528821).

21679939 is an equidigital number, since it uses as much as digits as its factorization.

21679939 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 528820.

The product of its digits is 183708, while the sum is 46.

The square root of 21679939 is about 4656.1721402886. The cubic root of 21679939 is about 278.8384662935.

The spelling of 21679939 in words is "twenty-one million, six hundred seventy-nine thousand, nine hundred thirty-nine".