21078979 has 4 divisors (see below), whose sum is σ = 21124584. Its totient is φ = 21033376.

The previous prime is 21078949. The next prime is 21078991. The reversal of 21078979 is 97987012.

It is a happy number.

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 21078979 - 2⁵ = 21078947 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21078919) 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, 22102 + ... + 23035.

It is an arithmetic number, because the mean of its divisors is an integer number (5281146).

Almost surely, 2^21078979 is an apocalyptic number.

21078979 is a deficient number, since it is larger than the sum of its proper divisors (45605).

21078979 is an equidigital number, since it uses as much as digits as its factorization.

21078979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45604.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 21078979 is about 4591.1849233068. The cubic root of 21078979 is about 276.2378533182.

The spelling of 21078979 in words is "twenty-one million, seventy-eight thousand, nine hundred seventy-nine".