21315817 has 8 divisors (see below), whose sum is σ = 22090752. Its totient is φ = 20546400.

The previous prime is 21315803. The next prime is 21315821. The reversal of 21315817 is 71851312.

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

It is a cyclic number.

It is not a de Polignac number, because 21315817 - 2⁷ = 21315689 is a prime.

It is a super-3 number, since 3×21315817³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21315517) 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, 7488 + ... + 9934.

It is an arithmetic number, because the mean of its divisors is an integer number (2761344).

Almost surely, 2^21315817 is an apocalyptic number.

It is an amenable number.

21315817 is a deficient number, since it is larger than the sum of its proper divisors (774935).

21315817 is a wasteful number, since it uses less digits than its factorization.

21315817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2759.

The product of its digits is 1680, while the sum is 28.

The square root of 21315817 is about 4616.9055654193. The cubic root of 21315817 is about 277.2685817855.

The spelling of 21315817 in words is "twenty-one million, three hundred fifteen thousand, eight hundred seventeen".