21865243 has 2 divisors, whose sum is σ = 21865244. Its totient is φ = 21865242.

The previous prime is 21865237. The next prime is 21865279. The reversal of 21865243 is 34256812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21865243 - 2⁵ = 21865211 is a prime.

It is not a weakly prime, because it can be changed into another prime (21865843) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932621 + 10932622.

It is an arithmetic number, because the mean of its divisors is an integer number (10932622).

Almost surely, 2^21865243 is an apocalyptic number.

21865243 is a deficient number, since it is larger than the sum of its proper divisors (1).

21865243 is an equidigital number, since it uses as much as digits as its factorization.

21865243 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11520, while the sum is 31.

The square root of 21865243 is about 4676.0285499556. The cubic root of 21865243 is about 279.6306482013.

The spelling of 21865243 in words is "twenty-one million, eight hundred sixty-five thousand, two hundred forty-three".