21355979 has 4 divisors (see below), whose sum is σ = 21758976. Its totient is φ = 20952984.

The previous prime is 21355969. The next prime is 21355987. The reversal of 21355979 is 97955312.

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 21355979 - 2⁴ = 21355963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21355909) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 201419 + ... + 201524.

It is an arithmetic number, because the mean of its divisors is an integer number (5439744).

Almost surely, 2^21355979 is an apocalyptic number.

21355979 is a deficient number, since it is larger than the sum of its proper divisors (402997).

21355979 is an equidigital number, since it uses as much as digits as its factorization.

21355979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 402996.

The product of its digits is 85050, while the sum is 41.

The square root of 21355979 is about 4621.2529686223. The cubic root of 21355979 is about 277.4426102136.

The spelling of 21355979 in words is "twenty-one million, three hundred fifty-five thousand, nine hundred seventy-nine".