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21828 = 22317107

21828 has 24 divisors (see below), whose sum is σ = 54432. Its totient is φ = 6784.

The previous prime is 21821. The next prime is 21839. The reversal of 21828 is 82812.

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 a nialpdrome in base 16.

It is a zygodrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (21821) by changing a digit.

21828 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 7 ways as a sum of consecutive naturals, for example, 151 + ... + 257.

It is an arithmetic number, because the mean of its divisors is an integer number (2268).

221828 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21828, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27216).

21828 is an abundant number, since it is smaller than the sum of its proper divisors (32604).

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

21828 is a wasteful number, since it uses less digits than its factorization.

21828 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 131 (or 129 counting only the distinct ones).

The product of its digits is 256, while the sum is 21.

The square root of 21828 is about 147.7430201397. The cubic root of 21828 is about 27.9471793305.

It can be divided in two parts, 2 and 1828, that added together give a triangular number (1830 = T60).

The spelling of 21828 in words is "twenty-one thousand, eight hundred twenty-eight".

Divisors: 1 2 3 4 6 12 17 34 51 68 102 107 204 214 321 428 642 1284 1819 3638 5457 7276 10914 21828