21357309 has 4 divisors (see below), whose sum is σ = 28476416. Its totient is φ = 14238204.

The previous prime is 21357299. The next prime is 21357313. The reversal of 21357309 is 90375312.

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 not a de Polignac number, because 21357309 - 2⁸ = 21357053 is a prime.

It is a super-2 number, since 2×21357309² = 912269295442962, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21357509) 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, 3559549 + ... + 3559554.

It is an arithmetic number, because the mean of its divisors is an integer number (7119104).

Almost surely, 2^21357309 is an apocalyptic number.

It is an amenable number.

21357309 is a deficient number, since it is larger than the sum of its proper divisors (7119107).

21357309 is an equidigital number, since it uses as much as digits as its factorization.

21357309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7119106.

The product of its (nonzero) digits is 5670, while the sum is 30.

The square root of 21357309 is about 4621.3968667493. The cubic root of 21357309 is about 277.4483695845.

The spelling of 21357309 in words is "twenty-one million, three hundred fifty-seven thousand, three hundred nine".