20121221 has 4 divisors (see below), whose sum is σ = 20376000. Its totient is φ = 19866444.

The previous prime is 20121193. The next prime is 20121271. The reversal of 20121221 is 12212102.

It is a happy number.

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 a de Polignac number, because none of the positive numbers 2^k-20121221 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20121271) 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, 127271 + ... + 127428.

It is an arithmetic number, because the mean of its divisors is an integer number (5094000).

Almost surely, 2^20121221 is an apocalyptic number.

It is an amenable number.

20121221 is a deficient number, since it is larger than the sum of its proper divisors (254779).

20121221 is an equidigital number, since it uses as much as digits as its factorization.

20121221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 254778.

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 20121221 is about 4485.6684005842. The cubic root of 20121221 is about 271.9890647637.

Adding to 20121221 its reverse (12212102), we get a palindrome (32333323).

The spelling of 20121221 in words is "twenty million, one hundred twenty-one thousand, two hundred twenty-one".