21905861 has 2 divisors, whose sum is σ = 21905862. Its totient is φ = 21905860.

The previous prime is 21905857. The next prime is 21905899. The reversal of 21905861 is 16850912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21104836 + 801025 = 4594^2 + 895^2 .

It is a cyclic number.

It is not a de Polignac number, because 21905861 - 2² = 21905857 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21905761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10952930 + 10952931.

It is an arithmetic number, because the mean of its divisors is an integer number (10952931).

Almost surely, 2^21905861 is an apocalyptic number.

It is an amenable number.

21905861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21905861 is an equidigital number, since it uses as much as digits as its factorization.

21905861 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21905861 is about 4680.3697503509. The cubic root of 21905861 is about 279.8036931846.

The spelling of 21905861 in words is "twenty-one million, nine hundred five thousand, eight hundred sixty-one".