21979138 has 4 divisors (see below), whose sum is σ = 32968710. Its totient is φ = 10989568.

The previous prime is 21979121. The next prime is 21979151. The reversal of 21979138 is 83197912.

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

It can be written as a sum of positive squares in only one way, i.e., 17665209 + 4313929 = 4203^2 + 2077^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21979138.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5494783 + ... + 5494786.

Almost surely, 2^21979138 is an apocalyptic number.

21979138 is a deficient number, since it is larger than the sum of its proper divisors (10989572).

21979138 is a wasteful number, since it uses less digits than its factorization.

21979138 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10989571.

The product of its digits is 27216, while the sum is 40.

The square root of 21979138 is about 4688.1913356859. The cubic root of 21979138 is about 280.1153351387.

The spelling of 21979138 in words is "twenty-one million, nine hundred seventy-nine thousand, one hundred thirty-eight".