21771979 has 4 divisors (see below), whose sum is σ = 22034376. Its totient is φ = 21509584.

The previous prime is 21771977. The next prime is 21771983. The reversal of 21771979 is 97917712.

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 21771979 - 2¹ = 21771977 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21771977) 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 3 ways as a sum of consecutive naturals, for example, 131074 + ... + 131239.

It is an arithmetic number, because the mean of its divisors is an integer number (5508594).

Almost surely, 2^21771979 is an apocalyptic number.

21771979 is a deficient number, since it is larger than the sum of its proper divisors (262397).

21771979 is an equidigital number, since it uses as much as digits as its factorization.

21771979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 262396.

The product of its digits is 55566, while the sum is 43.

The square root of 21771979 is about 4666.0453276838. The cubic root of 21771979 is about 279.2325027568.

The spelling of 21771979 in words is "twenty-one million, seven hundred seventy-one thousand, nine hundred seventy-nine".