21920309 has 4 divisors (see below), whose sum is σ = 21955680. Its totient is φ = 21884940.

The previous prime is 21920299. The next prime is 21920321. The reversal of 21920309 is 90302912.

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 a de Polignac number, because none of the positive numbers 2^k-21920309 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 (21920359) 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, 16739 + ... + 18000.

It is an arithmetic number, because the mean of its divisors is an integer number (5488920).

Almost surely, 2^21920309 is an apocalyptic number.

It is an amenable number.

21920309 is a deficient number, since it is larger than the sum of its proper divisors (35371).

21920309 is an equidigital number, since it uses as much as digits as its factorization.

21920309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35370.

The product of its (nonzero) digits is 972, while the sum is 26.

The square root of 21920309 is about 4681.9129637361. The cubic root of 21920309 is about 279.8651944623.

The spelling of 21920309 in words is "twenty-one million, nine hundred twenty thousand, three hundred nine".