21542 has 4 divisors (see below), whose sum is σ = 32316. Its totient is φ = 10770.

The previous prime is 21529. The next prime is 21557. The reversal of 21542 is 24512.

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

It is a congruent number.

It is an unprimeable number.

21542 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5384 + ... + 5387.

It is an arithmetic number, because the mean of its divisors is an integer number (8079).

2²¹⁵⁴² is an apocalyptic number.

21542 is a deficient number, since it is larger than the sum of its proper divisors (10774).

21542 is a wasteful number, since it uses less digits than its factorization.

21542 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10773.

The product of its digits is 80, while the sum is 14.

The square root of 21542 is about 146.7719319216. The cubic root of 21542 is about 27.8245836059.

Subtracting from 21542 its sum of digits (14), we obtain a triangular number (21528 = T₂₀₇).

The spelling of 21542 in words is "twenty-one thousand, five hundred forty-two".