21840817 has 2 divisors, whose sum is σ = 21840818. Its totient is φ = 21840816.

The previous prime is 21840809. The next prime is 21840829. The reversal of 21840817 is 71804812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20757136 + 1083681 = 4556^2 + 1041^2 .

It is a cyclic number.

It is not a de Polignac number, because 21840817 - 2³ = 21840809 is a prime.

It is not a weakly prime, because it can be changed into another prime (21840877) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10920408 + 10920409.

It is an arithmetic number, because the mean of its divisors is an integer number (10920409).

Almost surely, 2^21840817 is an apocalyptic number.

It is an amenable number.

21840817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21840817 is an equidigital number, since it uses as much as digits as its factorization.

21840817 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3584, while the sum is 31.

The square root of 21840817 is about 4673.4159883323. The cubic root of 21840817 is about 279.5264828343.

The spelling of 21840817 in words is "twenty-one million, eight hundred forty thousand, eight hundred seventeen".