21237 has 4 divisors (see below), whose sum is σ = 28320. Its totient is φ = 14156.

The previous prime is 21227. The next prime is 21247. The reversal of 21237 is 73212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21227) and next prime (21247).

It is a cyclic number.

It is not a de Polignac number, because 21237 - 2⁴ = 21221 is a prime.

It is a D-number.

It is a nialpdrome in base 13.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21237.

It is not an unprimeable number, because it can be changed into a prime (21227) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3537 + ... + 3542.

It is an arithmetic number, because the mean of its divisors is an integer number (7080).

2²¹²³⁷ is an apocalyptic number.

It is an amenable number.

21237 is a deficient number, since it is larger than the sum of its proper divisors (7083).

21237 is an equidigital number, since it uses as much as digits as its factorization.

21237 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7082.

The product of its digits is 84, while the sum is 15.

The square root of 21237 is about 145.7292009173. The cubic root of 21237 is about 27.6926418526.

Adding to 21237 its product of digits (84), we get a triangular number (21321 = T₂₀₆).

Adding to 21237 its reverse (73212), we get a palindrome (94449).

The spelling of 21237 in words is "twenty-one thousand, two hundred thirty-seven".