209861 has 2 divisors, whose sum is σ = 209862. Its totient is φ = 209860.

The previous prime is 209857. The next prime is 209887. The reversal of 209861 is 168902.

It is an a-pointer prime, because the next prime (209887) can be obtained adding 209861 to its sum of digits (26).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 172225 + 37636 = 415^2 + 194^2 .

It is a cyclic number.

It is not a de Polignac number, because 209861 - 2² = 209857 is a prime.

It is a Chen prime.

It is an Ulam number.

It is a self number, because there is not a number n which added to its sum of digits gives 209861.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 209861.

It is not a weakly prime, because it can be changed into another prime (209801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104930 + 104931.

It is an arithmetic number, because the mean of its divisors is an integer number (104931).

2²⁰⁹⁸⁶¹ is an apocalyptic number.

It is an amenable number.

209861 is a deficient number, since it is larger than the sum of its proper divisors (1).

209861 is an equidigital number, since it uses as much as digits as its factorization.

209861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 209861 is about 458.1058829572. The cubic root of 209861 is about 59.4261022656.

The spelling of 209861 in words is "two hundred nine thousand, eight hundred sixty-one".