21213 has 6 divisors (see below), whose sum is σ = 30654. Its totient is φ = 14136.

The previous prime is 21211. The next prime is 21221. The reversal of 21213 is 31212.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 15129 + 6084 = 123^2 + 78^2 .

It is not a de Polignac number, because 21213 - 2¹ = 21211 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: 2357 = 21213 / (2 + 1 + 2 + 1 + 3).

It is a nialpdrome in base 15.

It is a junction number, because it is equal to n+sod(n) for n = 21195 and 21204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21211) 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, 1170 + ... + 1187.

It is an arithmetic number, because the mean of its divisors is an integer number (5109).

2²¹²¹³ is an apocalyptic number.

It is an amenable number.

21213 is a deficient number, since it is larger than the sum of its proper divisors (9441).

21213 is a wasteful number, since it uses less digits than its factorization.

21213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2363 (or 2360 counting only the distinct ones).

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

The square root of 21213 is about 145.6468331273. The cubic root of 21213 is about 27.6822060734.

Adding to 21213 its reverse (31212), we get a palindrome (52425).

Subtracting 21213 from its reverse (31212), we obtain a palindrome (9999).

It can be divided in two parts, 212 and 13, that added together give a square (225 = 15²).

The spelling of 21213 in words is "twenty-one thousand, two hundred thirteen".