21221 has 2 divisors, whose sum is σ = 21222. Its totient is φ = 21220.

The previous prime is 21211. The next prime is 21227. The reversal of 21221 is 12212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21025 + 196 = 145^2 + 14^2 .

It is a cyclic number.

It is not a de Polignac number, because 21221 - 2⁶ = 21157 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a nialpdrome in base 13.

It is a junction number, because it is equal to n+sod(n) for n = 21199 and 21208.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610 + 10611.

It is an arithmetic number, because the mean of its divisors is an integer number (10611).

2²¹²²¹ is an apocalyptic number.

It is an amenable number.

21221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221 is an equidigital number, since it uses as much as digits as its factorization.

21221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8, while the sum is 8.

The square root of 21221 is about 145.6742942320. The cubic root of 21221 is about 27.6856855406.

Adding to 21221 its reverse (12212), we get a palindrome (33433).

Subtracting from 21221 its reverse (12212), we obtain a palindrome (9009).

It can be divided in two parts, 21 and 221, that added together give a palindrome (242).

The spelling of 21221 in words is "twenty-one thousand, two hundred twenty-one", and thus it is an iban number.