21704857 has 2 divisors, whose sum is σ = 21704858. Its totient is φ = 21704856.

The previous prime is 21704833. The next prime is 21704887. The reversal of 21704857 is 75840712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20214016 + 1490841 = 4496^2 + 1221^2 .

It is a cyclic number.

It is not a de Polignac number, because 21704857 - 2¹¹ = 21702809 is a prime.

It is a super-2 number, since 2×21704857² = 942201634780898, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21704887) 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, 10852428 + 10852429.

It is an arithmetic number, because the mean of its divisors is an integer number (10852429).

Almost surely, 2^21704857 is an apocalyptic number.

It is an amenable number.

21704857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21704857 is an equidigital number, since it uses as much as digits as its factorization.

21704857 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 15680, while the sum is 34.

The square root of 21704857 is about 4658.8471749994. The cubic root of 21704857 is about 278.9452537504.

The spelling of 21704857 in words is "twenty-one million, seven hundred four thousand, eight hundred fifty-seven".