20021221 has 4 divisors (see below), whose sum is σ = 21841344. Its totient is φ = 18201100.

The previous prime is 20021213. The next prime is 20021233. The reversal of 20021221 is 12212002.

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 20021221 - 2³ = 20021213 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20021198 and 20021207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20021251) 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, 910045 + ... + 910066.

It is an arithmetic number, because the mean of its divisors is an integer number (5460336).

Almost surely, 2^20021221 is an apocalyptic number.

It is an amenable number.

20021221 is a deficient number, since it is larger than the sum of its proper divisors (1820123).

20021221 is a wasteful number, since it uses less digits than its factorization.

20021221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1820122.

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

The square root of 20021221 is about 4474.5079059043. The cubic root of 20021221 is about 271.5377321514.

Adding to 20021221 its reverse (12212002), we get a palindrome (32233223).

It can be divided in two parts, 2002 and 1221, that multiplied together give a palindrome (2444442).

The spelling of 20021221 in words is "twenty million, twenty-one thousand, two hundred twenty-one".