21018857 has 2 divisors, whose sum is σ = 21018858. Its totient is φ = 21018856.

The previous prime is 21018841. The next prime is 21018859. The reversal of 21018857 is 75881012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17673616 + 3345241 = 4204^2 + 1829^2 .

It is a cyclic number.

It is not a de Polignac number, because 21018857 - 2⁴ = 21018841 is a prime.

Together with 21018859, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21018859) 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, 10509428 + 10509429.

It is an arithmetic number, because the mean of its divisors is an integer number (10509429).

Almost surely, 2^21018857 is an apocalyptic number.

It is an amenable number.

21018857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21018857 is an equidigital number, since it uses as much as digits as its factorization.

21018857 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4480, while the sum is 32.

The square root of 21018857 is about 4584.6327006643. The cubic root of 21018857 is about 275.9749723507.

Adding to 21018857 its reverse (75881012), we get a palindrome (96899869).

The spelling of 21018857 in words is "twenty-one million, eighteen thousand, eight hundred fifty-seven".