21936 has 20 divisors (see below), whose sum is σ = 56792. Its totient is φ = 7296.

The previous prime is 21929. The next prime is 21937. The reversal of 21936 is 63912.

21936 = 9² + 10² + ... + 40².

21936 is nontrivially palindromic in base 15.

It is a hoax number, since the sum of its digits (21) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21937) 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 3 ways as a sum of consecutive naturals, for example, 181 + ... + 276.

2²¹⁹³⁶ is an apocalyptic number.

It is an amenable number.

21936 is an abundant number, since it is smaller than the sum of its proper divisors (34856).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28396).

21936 is a wasteful number, since it uses less digits than its factorization.

21936 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 468 (or 462 counting only the distinct ones).

The product of its digits is 324, while the sum is 21.

The square root of 21936 is about 148.1080686526. The cubic root of 21936 is about 27.9931956255.

Subtracting from 21936 its product of digits (324), we obtain a palindrome (21612).

The spelling of 21936 in words is "twenty-one thousand, nine hundred thirty-six".