20201221 has 4 divisors (see below), whose sum is σ = 20211232. Its totient is φ = 20191212.

The previous prime is 20201191. The next prime is 20201227. The reversal of 20201221 is 12210202.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12210202 = 2 ⋅6105101.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20201221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20201198 and 20201207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20201227) 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, 801 + ... + 6406.

It is an arithmetic number, because the mean of its divisors is an integer number (5052808).

Almost surely, 2^20201221 is an apocalyptic number.

It is an amenable number.

20201221 is a deficient number, since it is larger than the sum of its proper divisors (10011).

20201221 is an equidigital number, since it uses as much as digits as its factorization.

20201221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10010.

The product of its (nonzero) digits is 16, while the sum is 10.

The square root of 20201221 is about 4494.5768432634. The cubic root of 20201221 is about 272.3490553648.

Adding to 20201221 its reverse (12210202), we get a palindrome (32411423).

The spelling of 20201221 in words is "twenty million, two hundred one thousand, two hundred twenty-one".