21431 has 4 divisors (see below), whose sum is σ = 22200. Its totient is φ = 20664.

The previous prime is 21419. The next prime is 21433. The reversal of 21431 is 13412.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21431 - 2¹⁰ = 20407 is a prime.

It is a super-2 number, since 2×21431² = 918575522, which contains 22 as substring.

It is a Duffinian number.

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 21431.

It is not an unprimeable number, because it can be changed into a prime (21433) 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, 341 + ... + 398.

It is an arithmetic number, because the mean of its divisors is an integer number (5550).

2²¹⁴³¹ is an apocalyptic number.

21431 is a deficient number, since it is larger than the sum of its proper divisors (769).

21431 is an equidigital number, since it uses as much as digits as its factorization.

21431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 768.

The product of its digits is 24, while the sum is 11.

The square root of 21431 is about 146.3933058579. The cubic root of 21431 is about 27.7767104775.

Adding to 21431 its reverse (13412), we get a palindrome (34843).

The spelling of 21431 in words is "twenty-one thousand, four hundred thirty-one".