21409979 has 16 divisors (see below), whose sum is σ = 23328000. Its totient is φ = 19585440.

The previous prime is 21409931. The next prime is 21409991. The reversal of 21409979 is 97990412.

It is a happy number.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21409979 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21409909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 79457 + ... + 79725.

It is an arithmetic number, because the mean of its divisors is an integer number (1458000).

Almost surely, 2^21409979 is an apocalyptic number.

21409979 is a deficient number, since it is larger than the sum of its proper divisors (1918021).

21409979 is a wasteful number, since it uses less digits than its factorization.

21409979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 418.

The product of its (nonzero) digits is 40824, while the sum is 41.

The square root of 21409979 is about 4627.0918512604. The cubic root of 21409979 is about 277.6762573667.

The spelling of 21409979 in words is "twenty-one million, four hundred nine thousand, nine hundred seventy-nine".