21051979 has 4 divisors (see below), whose sum is σ = 22671376. Its totient is φ = 19432584.

The previous prime is 21051977. The next prime is 21051991. The reversal of 21051979 is 97915012.

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

It is a cyclic number.

It is not a de Polignac number, because 21051979 - 2¹ = 21051977 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21051977) 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, 809679 + ... + 809704.

It is an arithmetic number, because the mean of its divisors is an integer number (5667844).

Almost surely, 2^21051979 is an apocalyptic number.

21051979 is a deficient number, since it is larger than the sum of its proper divisors (1619397).

21051979 is a wasteful number, since it uses less digits than its factorization.

21051979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1619396.

The product of its (nonzero) digits is 5670, while the sum is 34.

The square root of 21051979 is about 4588.2435637180. The cubic root of 21051979 is about 276.1198588493.

The spelling of 21051979 in words is "twenty-one million, fifty-one thousand, nine hundred seventy-nine".