21865891 has 2 divisors, whose sum is σ = 21865892. Its totient is φ = 21865890.

The previous prime is 21865843. The next prime is 21865901. The reversal of 21865891 is 19856812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21865891 - 2⁹ = 21865379 is a prime.

It is not a weakly prime, because it can be changed into another prime (21865841) 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, 10932945 + 10932946.

It is an arithmetic number, because the mean of its divisors is an integer number (10932946).

Almost surely, 2^21865891 is an apocalyptic number.

21865891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21865891 is an equidigital number, since it uses as much as digits as its factorization.

21865891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34560, while the sum is 40.

The square root of 21865891 is about 4676.0978390106. The cubic root of 21865891 is about 279.6334105591.

The spelling of 21865891 in words is "twenty-one million, eight hundred sixty-five thousand, eight hundred ninety-one".