21316809 has 8 divisors (see below), whose sum is σ = 29339392. Its totient is φ = 13752720.

The previous prime is 21316783. The next prime is 21316819. The reversal of 21316809 is 90861312.

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

It is not a de Polignac number, because 21316809 - 2⁸ = 21316553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21316819) 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, 114514 + ... + 114699.

It is an arithmetic number, because the mean of its divisors is an integer number (3667424).

Almost surely, 2^21316809 is an apocalyptic number.

It is an amenable number.

21316809 is a deficient number, since it is larger than the sum of its proper divisors (8022583).

21316809 is a wasteful number, since it uses less digits than its factorization.

21316809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 229247.

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 21316809 is about 4617.0129954333. The cubic root of 21316809 is about 277.2728829134.

The spelling of 21316809 in words is "twenty-one million, three hundred sixteen thousand, eight hundred nine".