210905 has 4 divisors (see below), whose sum is σ = 253092. Its totient is φ = 168720.

The previous prime is 210901. The next prime is 210907. The reversal of 210905 is 509012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 35344 + 175561 = 188^2 + 419^2 .

It is not a de Polignac number, because 210905 - 2² = 210901 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (210901) 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, 21086 + ... + 21095.

It is an arithmetic number, because the mean of its divisors is an integer number (63273).

2²¹⁰⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

210905 is a deficient number, since it is larger than the sum of its proper divisors (42187).

210905 is an equidigital number, since it uses as much as digits as its factorization.

210905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42186.

The product of its (nonzero) digits is 90, while the sum is 17.

The square root of 210905 is about 459.2439438904. The cubic root of 210905 is about 59.5244820749.

Adding to 210905 its reverse (509012), we get a palindrome (719917).

The spelling of 210905 in words is "two hundred ten thousand, nine hundred five".