20221 has 4 divisors (see below), whose sum is σ = 20572.
Its totient is φ = 19872.
The previous prime is 20219. The next prime is 20231. The reversal of 20221 is 12202.
It is a happy number.
It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12202 = 2 ⋅6101.
It can be written as a sum of positive squares in 2 ways, for example, as 7225 + 12996 = 85^2 + 114^2
It is a cyclic number.
It is not a de Polignac number, because 20221 - 21 = 20219 is a prime.
It is a Duffinian number.
It is a nialpdrome in base 12.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (20201) 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, 66 + ... + 211.
It is an arithmetic number, because the mean of its divisors is an integer number (5143).
220221 is an apocalyptic number.
It is an amenable number.
20221 is a deficient number, since it is larger than the sum of its proper divisors (351).
20221 is an equidigital number, since it uses as much as digits as its factorization.
With its predecessor (20220) it forms an eRAP, since the sums of their prime factors are consecutive (349 and 350).
20221 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 350.
The product of its (nonzero) digits is 8, while the sum is 7.
The square root of 20221 is about 142.2005625868.
The cubic root of 20221 is about 27.2437911955.
Adding to 20221 its reverse (12202), we get a palindrome (32423).
The spelling of 20221 in words is "twenty thousand, two hundred twenty-one", and thus it is an iban number.