21992909 has 4 divisors (see below), whose sum is σ = 22504416. Its totient is φ = 21481404.

The previous prime is 21992897. The next prime is 21992923. The reversal of 21992909 is 90929912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21992909 - 2⁸ = 21992653 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21992989) 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, 255689 + ... + 255774.

It is an arithmetic number, because the mean of its divisors is an integer number (5626104).

Almost surely, 2^21992909 is an apocalyptic number.

It is an amenable number.

21992909 is a deficient number, since it is larger than the sum of its proper divisors (511507).

21992909 is an equidigital number, since it uses as much as digits as its factorization.

21992909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 511506.

The product of its (nonzero) digits is 26244, while the sum is 41.

The square root of 21992909 is about 4689.6597957634. The cubic root of 21992909 is about 280.1738248898.

The spelling of 21992909 in words is "twenty-one million, nine hundred ninety-two thousand, nine hundred nine".