21994309 has 4 divisors (see below), whose sum is σ = 22304160. Its totient is φ = 21684460.

The previous prime is 21994237. The next prime is 21994319. The reversal of 21994309 is 90349912.

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-21994309 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 (21994319) 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, 154819 + ... + 154960.

It is an arithmetic number, because the mean of its divisors is an integer number (5576040).

Almost surely, 2^21994309 is an apocalyptic number.

It is an amenable number.

21994309 is a deficient number, since it is larger than the sum of its proper divisors (309851).

21994309 is an equidigital number, since it uses as much as digits as its factorization.

21994309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 309850.

The product of its (nonzero) digits is 17496, while the sum is 37.

The square root of 21994309 is about 4689.8090579468. The cubic root of 21994309 is about 280.1797697609.

The spelling of 21994309 in words is "twenty-one million, nine hundred ninety-four thousand, three hundred nine".