21544 has 8 divisors (see below), whose sum is σ = 40410. Its totient is φ = 10768.

The previous prime is 21529. The next prime is 21557. The reversal of 21544 is 44512.

It can be written as a sum of positive squares in only one way, i.e., 19044 + 2500 = 138^2 + 50^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a plaindrome in base 14.

It is an unprimeable number.

21544 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1339 + ... + 1354.

2²¹⁵⁴⁴ is an apocalyptic number.

It is an amenable number.

21544 is a deficient number, since it is larger than the sum of its proper divisors (18866).

21544 is a wasteful number, since it uses less digits than its factorization.

21544 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2699 (or 2695 counting only the distinct ones).

The product of its digits is 160, while the sum is 16.

The square root of 21544 is about 146.7787450553. The cubic root of 21544 is about 27.8254446749.

Subtracting from 21544 its sum of digits (16), we obtain a triangular number (21528 = T₂₀₇).

It can be divided in two parts, 21 and 544, that added together give a palindrome (565).

The spelling of 21544 in words is "twenty-one thousand, five hundred forty-four".