209881 has 4 divisors (see below), whose sum is σ = 239872. Its totient is φ = 179892.

The previous prime is 209861. The next prime is 209887. The reversal of 209881 is 188902.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 209881 - 2¹¹ = 207833 is a prime.

It is a super-2 number, since 2×209881² = 88100068322, which contains 22 as substring.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (209887) 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 in 3 ways as a sum of consecutive naturals, for example, 14985 + ... + 14998.

It is an arithmetic number, because the mean of its divisors is an integer number (59968).

2²⁰⁹⁸⁸¹ is an apocalyptic number.

209881 is the 265-th hex number.

It is an amenable number.

209881 is a deficient number, since it is larger than the sum of its proper divisors (29991).

209881 is an equidigital number, since it uses as much as digits as its factorization.

209881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29990.

The product of its (nonzero) digits is 1152, while the sum is 28.

The square root of 209881 is about 458.1277114517. The cubic root of 209881 is about 59.4279899981.

The spelling of 209881 in words is "two hundred nine thousand, eight hundred eighty-one".