21979805 has 8 divisors (see below), whose sum is σ = 26513592. Its totient is φ = 17491968.

The previous prime is 21979787. The next prime is 21979807. The reversal of 21979805 is 50897912.

It can be written as a sum of positive squares in 4 ways, for example, as 3644281 + 18335524 = 1909^2 + 4282^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21979805 is a prime.

It is a super-2 number, since 2×21979805² = 966223655676050, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979807) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10424 + ... + 12353.

It is an arithmetic number, because the mean of its divisors is an integer number (3314199).

Almost surely, 2^21979805 is an apocalyptic number.

It is an amenable number.

21979805 is a deficient number, since it is larger than the sum of its proper divisors (4533787).

21979805 is a wasteful number, since it uses less digits than its factorization.

21979805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22975.

The product of its (nonzero) digits is 45360, while the sum is 41.

The square root of 21979805 is about 4688.2624713213. The cubic root of 21979805 is about 280.1181686596.

The spelling of 21979805 in words is "twenty-one million, nine hundred seventy-nine thousand, eight hundred five".