21121 has 2 divisors, whose sum is σ = 21122. Its totient is φ = 21120.

The previous prime is 21107. The next prime is 21139. The reversal of 21121 is 12112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19600 + 1521 = 140^2 + 39^2 .

It is a cyclic number.

It is not a de Polignac number, because 21121 - 2⁵ = 21089 is a prime.

It is not a weakly prime, because it can be changed into another prime (21101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560 + 10561.

It is an arithmetic number, because the mean of its divisors is an integer number (10561).

2²¹¹²¹ is an apocalyptic number.

It is an amenable number.

21121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121 is an equidigital number, since it uses as much as digits as its factorization.

21121 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4, while the sum is 7.

The square root of 21121 is about 145.3306574677. The cubic root of 21121 is about 27.6421291773.

Adding to 21121 its reverse (12112), we get a palindrome (33233).

Subtracting from 21121 its reverse (12112), we obtain a palindrome (9009).

It can be divided in two parts, 211 and 21, that added together give a palindrome (232).

The spelling of 21121 in words is "twenty-one thousand, one hundred twenty-one", and thus it is an iban number.