209831 has 4 divisors (see below), whose sum is σ = 222192. Its totient is φ = 197472.

The previous prime is 209821. The next prime is 209837. The reversal of 209831 is 138902.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 209831 - 2⁶ = 209767 is a prime.

It is a super-2 number, since 2×209831² = 88058097122, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 14.

It is a junction number, because it is equal to n+sod(n) for n = 209797 and 209806.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209837) 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, 6155 + ... + 6188.

It is an arithmetic number, because the mean of its divisors is an integer number (55548).

2²⁰⁹⁸³¹ is an apocalyptic number.

209831 is a deficient number, since it is larger than the sum of its proper divisors (12361).

209831 is a wasteful number, since it uses less digits than its factorization.

209831 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12360.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 209831 is about 458.0731382651. The cubic root of 209831 is about 59.4232704420.

The spelling of 209831 in words is "two hundred nine thousand, eight hundred thirty-one".