21546 has 40 divisors (see below), whose sum is σ = 58080. Its totient is φ = 5832.

The previous prime is 21529. The next prime is 21557. The reversal of 21546 is 64512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

Its product of digits (240) is a multiple of the sum of its prime factors (40).

It is a Curzon number.

It is a zygodrome in base 4.

It is an unprimeable number.

21546 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 in 19 ways as a sum of consecutive naturals, for example, 1125 + ... + 1143.

It is an arithmetic number, because the mean of its divisors is an integer number (1452).

2²¹⁵⁴⁶ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21546, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29040).

21546 is an abundant number, since it is smaller than the sum of its proper divisors (36534).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21546 is a wasteful number, since it uses less digits than its factorization.

21546 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40 (or 31 counting only the distinct ones).

The product of its digits is 240, while the sum is 18.

The square root of 21546 is about 146.7855578727. The cubic root of 21546 is about 27.8263056906.

Subtracting from 21546 its sum of digits (18), we obtain a triangular number (21528 = T₂₀₇).

The spelling of 21546 in words is "twenty-one thousand, five hundred forty-six".