21856817 has 2 divisors, whose sum is σ = 21856818. Its totient is φ = 21856816.

The previous prime is 21856811. The next prime is 21856837. The reversal of 21856817 is 71865812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16516096 + 5340721 = 4064^2 + 2311^2 .

It is a cyclic number.

It is not a de Polignac number, because 21856817 - 2⁴ = 21856801 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21856811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10928408 + 10928409.

It is an arithmetic number, because the mean of its divisors is an integer number (10928409).

Almost surely, 2^21856817 is an apocalyptic number.

It is an amenable number.

21856817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21856817 is an equidigital number, since it uses as much as digits as its factorization.

21856817 is an evil number, because the sum of its binary digits is even.

The product of its digits is 26880, while the sum is 38.

The square root of 21856817 is about 4675.1274848928. The cubic root of 21856817 is about 279.5947240551.

The spelling of 21856817 in words is "twenty-one million, eight hundred fifty-six thousand, eight hundred seventeen".