21504 has 44 divisors (see below), whose sum is σ = 65504. Its totient is φ = 6144.

The previous prime is 21503. The next prime is 21517. The reversal of 21504 is 40512.

It is a hoax number, since the sum of its digits (12) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a nialpdrome in base 4, base 8 and base 16.

It is a zygodrome in base 4.

It is a self number, because there is not a number *n* which added to its sum of digits gives 21504.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3069 + ... + 3075.

21504 is a Friedman number, since it can be written as 21*(4+0)^5, using all its digits and the basic arithmetic operations.

2^{21504} is an apocalyptic number.

21504 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21504, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32752).

21504 is an abundant number, since it is smaller than the sum of its proper divisors (44000).

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

21504 is an equidigital number, since it uses as much as digits as its factorization.

21504 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30 (or 12 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 12.

The square root of 21504 is about 146.6424222386. The cubic root of 21504 is about 27.8082131591.

It can be divided in two parts, 21 and 504, that added together give a palindrome (525).

The spelling of 21504 in words is "twenty-one thousand, five hundred four".

Divisors: 1 2 3 4 6 7 8 12 14 16 21 24 28 32 42 48 56 64 84 96 112 128 168 192 224 256 336 384 448 512 672 768 896 1024 1344 1536 1792 2688 3072 3584 5376 7168 10752 21504

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