209857 has 2 divisors, whose sum is σ = 209858. Its totient is φ = 209856.

The previous prime is 209851. The next prime is 209861. The reversal of 209857 is 758902.

209857 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 194481 + 15376 = 441^2 + 124^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-209857 is a prime.

209857 is a lucky number.

It is a plaindrome in base 14.

It is not a weakly prime, because it can be changed into another prime (209851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104928 + 104929.

It is an arithmetic number, because the mean of its divisors is an integer number (104929).

2²⁰⁹⁸⁵⁷ is an apocalyptic number.

It is an amenable number.

209857 is a deficient number, since it is larger than the sum of its proper divisors (1).

209857 is an equidigital number, since it uses as much as digits as its factorization.

209857 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5040, while the sum is 31.

The square root of 209857 is about 458.1015171335. The cubic root of 209857 is about 59.4257247047.

The spelling of 209857 in words is "two hundred nine thousand, eight hundred fifty-seven".