21543 has 8 divisors (see below), whose sum is σ = 29568. Its totient is φ = 13944.

The previous prime is 21529. The next prime is 21557. The reversal of 21543 is 34512.

It is an interprime number because it is at equal distance from previous prime (21529) and next prime (21557).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21543 - 2⁹ = 21031 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21503) 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 7 ways as a sum of consecutive naturals, for example, 46 + ... + 212.

It is an arithmetic number, because the mean of its divisors is an integer number (3696).

2²¹⁵⁴³ is an apocalyptic number.

21543 is a deficient number, since it is larger than the sum of its proper divisors (8025).

21543 is a wasteful number, since it uses less digits than its factorization.

21543 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 213.

The product of its digits is 120, while the sum is 15.

The square root of 21543 is about 146.7753385280. The cubic root of 21543 is about 27.8250141471.

Subtracting from 21543 its sum of digits (15), we obtain a triangular number (21528 = T₂₀₇).

The spelling of 21543 in words is "twenty-one thousand, five hundred forty-three".