21549 has 8 divisors (see below), whose sum is σ = 31392. Its totient is φ = 13040.

The previous prime is 21529. The next prime is 21557. The reversal of 21549 is 94512.

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

It is a cyclic number.

It is not a de Polignac number, because 21549 - 2⁵ = 21517 is a prime.

21549 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21529) 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, 294 + ... + 359.

It is an arithmetic number, because the mean of its divisors is an integer number (3924).

2²¹⁵⁴⁹ is an apocalyptic number.

It is an amenable number.

21549 is a deficient number, since it is larger than the sum of its proper divisors (9843).

21549 is a wasteful number, since it uses less digits than its factorization.

21549 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 667.

The product of its digits is 360, while the sum is 21.

The square root of 21549 is about 146.7957765060. The cubic root of 21549 is about 27.8275971143.

Subtracting from 21549 its sum of digits (21), we obtain a triangular number (21528 = T₂₀₇).

It can be divided in two parts, 2 and 1549, that added together give a palindrome (1551).

The spelling of 21549 in words is "twenty-one thousand, five hundred forty-nine".