21639279 has 8 divisors (see below), whose sum is σ = 28926640. Its totient is φ = 14389056.

The previous prime is 21639269. The next prime is 21639281. The reversal of 21639279 is 97293612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21639279 - 2⁴ = 21639263 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21639259) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7894 + ... + 10275.

It is an arithmetic number, because the mean of its divisors is an integer number (3615830).

Almost surely, 2^21639279 is an apocalyptic number.

21639279 is a deficient number, since it is larger than the sum of its proper divisors (7287361).

21639279 is a wasteful number, since it uses less digits than its factorization.

21639279 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18569.

The product of its digits is 40824, while the sum is 39.

The square root of 21639279 is about 4651.8038436718. The cubic root of 21639279 is about 278.6640398006.

The spelling of 21639279 in words is "twenty-one million, six hundred thirty-nine thousand, two hundred seventy-nine".