21243857 has 2 divisors, whose sum is σ = 21243858. Its totient is φ = 21243856.

The previous prime is 21243841. The next prime is 21243907. The reversal of 21243857 is 75834212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18671041 + 2572816 = 4321^2 + 1604^2 .

It is a cyclic number.

It is not a de Polignac number, because 21243857 - 2⁴ = 21243841 is a prime.

It is not a weakly prime, because it can be changed into another prime (21242857) 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, 10621928 + 10621929.

It is an arithmetic number, because the mean of its divisors is an integer number (10621929).

Almost surely, 2^21243857 is an apocalyptic number.

It is an amenable number.

21243857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21243857 is an equidigital number, since it uses as much as digits as its factorization.

21243857 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13440, while the sum is 32.

The square root of 21243857 is about 4609.1058785843. The cubic root of 21243857 is about 276.9562199747.

The spelling of 21243857 in words is "twenty-one million, two hundred forty-three thousand, eight hundred fifty-seven".