209681 has 4 divisors (see below), whose sum is σ = 210672. Its totient is φ = 208692.

The previous prime is 209669. The next prime is 209687. The reversal of 209681 is 186902.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 209681 - 2¹⁰ = 208657 is a prime.

It is a super-2 number, since 2×209681² = 87932243522, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a nialpdrome in base 16.

It is a zygodrome in base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 209681.

It is not an unprimeable number, because it can be changed into a prime (209687) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 35 + ... + 648.

It is an arithmetic number, because the mean of its divisors is an integer number (52668).

2²⁰⁹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

209681 is a deficient number, since it is larger than the sum of its proper divisors (991).

209681 is an equidigital number, since it uses as much as digits as its factorization.

209681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 990.

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

The square root of 209681 is about 457.9093796812. The cubic root of 209681 is about 59.4091072735.

The spelling of 209681 in words is "two hundred nine thousand, six hundred eighty-one".