21231 has 12 divisors (see below), whose sum is σ = 35152. Its totient is φ = 12096.

The previous prime is 21227. The next prime is 21247. The reversal of 21231 is 13212.

It is a happy number.

It is not a de Polignac number, because 21231 - 2² = 21227 is a prime.

It is a super-2 number, since 2×21231² = 901510722, which contains 22 as substring.

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

It is a Duffinian number.

21231 is a lucky number.

It is a nialpdrome in base 9 and base 13.

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 11 ways as a sum of consecutive naturals, for example, 106 + ... + 231.

2²¹²³¹ is an apocalyptic number.

21231 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21231 is a deficient number, since it is larger than the sum of its proper divisors (13921).

21231 is a wasteful number, since it uses less digits than its factorization.

21231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 350 (or 347 counting only the distinct ones).

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

The square root of 21231 is about 145.7086133350. The cubic root of 21231 is about 27.6900336452.

Adding to 21231 its reverse (13212), we get a palindrome (34443).

It can be divided in two parts, 212 and 31, that added together give a 5-th power (243 = 3⁵).

The spelling of 21231 in words is "twenty-one thousand, two hundred thirty-one".