210821 has 4 divisors (see below), whose sum is σ = 227052. Its totient is φ = 194592.

The previous prime is 210811. The next prime is 210823. The reversal of 210821 is 128012.

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 98596 + 112225 = 314^2 + 335^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-210821 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 210796 and 210805.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (210823) 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, 8096 + ... + 8121.

It is an arithmetic number, because the mean of its divisors is an integer number (56763).

2²¹⁰⁸²¹ is an apocalyptic number.

It is an amenable number.

210821 is a deficient number, since it is larger than the sum of its proper divisors (16231).

210821 is a wasteful number, since it uses less digits than its factorization.

210821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16230.

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 210821 is about 459.1524801196. The cubic root of 210821 is about 59.5165784841.

Adding to 210821 its reverse (128012), we get a palindrome (338833).

The spelling of 210821 in words is "two hundred ten thousand, eight hundred twenty-one".