21321 has 12 divisors (see below), whose sum is σ = 32448. Its totient is φ = 13464.

The previous prime is 21319. The next prime is 21323. The reversal of 21321 is 12312.

21321 = 14² + 15² + ... + 40².

It is a happy number.

21321 is a nontrivial binomial coefficient, being equal to C(207, 2).

It is an interprime number because it is at equal distance from previous prime (21319) and next prime (21323).

It is not a de Polignac number, because 21321 - 2¹ = 21319 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a D-number.

It is a Curzon number.

It is a plaindrome in base 14.

It is a nialpdrome in base 9 and base 13.

It is not an unprimeable number, because it can be changed into a prime (21323) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 156 + ... + 258.

It is an arithmetic number, because the mean of its divisors is an integer number (2704).

2²¹³²¹ is an apocalyptic number.

21321 is the 206-th triangular number.

It is an amenable number.

21321 is a deficient number, since it is larger than the sum of its proper divisors (11127).

21321 is a wasteful number, since it uses less digits than its factorization.

21321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132 (or 129 counting only the distinct ones).

The product of its digits is 12, while the sum is 9.

The square root of 21321 is about 146.0171222837. The cubic root of 21321 is about 27.7291052839.

Adding to 21321 its reverse (12312), we get a palindrome (33633).

Subtracting from 21321 its reverse (12312), we obtain a palindrome (9009).

The spelling of 21321 in words is "twenty-one thousand, three hundred twenty-one", and thus it is an iban number.