220821 has 4 divisors (see below), whose sum is σ = 294432. Its totient is φ = 147212.

The previous prime is 220811. The next prime is 220841. The reversal of 220821 is 128022.

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 220821 - 2⁵ = 220789 is a prime.

It is a D-number.

It is a plaindrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 220821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (220811) 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, 36801 + ... + 36806.

It is an arithmetic number, because the mean of its divisors is an integer number (73608).

2²²⁰⁸²¹ is an apocalyptic number.

It is an amenable number.

220821 is a deficient number, since it is larger than the sum of its proper divisors (73611).

220821 is an equidigital number, since it uses as much as digits as its factorization.

220821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73610.

The product of its (nonzero) digits is 64, while the sum is 15.

The square root of 220821 is about 469.9159499315. The cubic root of 220821 is about 60.4431084153.

Adding to 220821 its reverse (128022), we get a palindrome (348843).

The spelling of 220821 in words is "two hundred twenty thousand, eight hundred twenty-one".