21138879 has 8 divisors (see below), whose sum is σ = 28647472. Its totient is φ = 13861440.

The previous prime is 21138853. The next prime is 21138881. The reversal of 21138879 is 97883112.

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

It is not a de Polignac number, because 21138879 - 2⁵ = 21138847 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 (21138179) 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, 57574 + ... + 57939.

It is an arithmetic number, because the mean of its divisors is an integer number (3580934).

Almost surely, 2^21138879 is an apocalyptic number.

21138879 is a deficient number, since it is larger than the sum of its proper divisors (7508593).

21138879 is a wasteful number, since it uses less digits than its factorization.

21138879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 115577.

The product of its digits is 24192, while the sum is 39.

The square root of 21138879 is about 4597.7036659620. The cubic root of 21138879 is about 276.4992669697.

The spelling of 21138879 in words is "twenty-one million, one hundred thirty-eight thousand, eight hundred seventy-nine".