20011221 has 6 divisors (see below), whose sum is σ = 28905110. Its totient is φ = 13340808.

The previous prime is 20011177. The next prime is 20011249. The reversal of 20011221 is 12211002.

It can be written as a sum of positive squares in only one way, i.e., 14062500 + 5948721 = 3750^2 + 2439^2 .

It is not a de Polignac number, because 20011221 - 2⁷ = 20011093 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 2223469 = 20011221 / (2 + 0 + 0 + 1 + 1 + 2 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20011291) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1111726 + ... + 1111743.

Almost surely, 2^20011221 is an apocalyptic number.

It is an amenable number.

20011221 is a deficient number, since it is larger than the sum of its proper divisors (8893889).

20011221 is a wasteful number, since it uses less digits than its factorization.

20011221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2223475 (or 2223472 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 20011221 is about 4473.3903250220. The cubic root of 20011221 is about 271.4925163022.

Adding to 20011221 its reverse (12211002), we get a palindrome (32222223).

The spelling of 20011221 in words is "twenty million, eleven thousand, two hundred twenty-one".