21100 has 18 divisors (see below), whose sum is σ = 46004. Its totient is φ = 8400.

The previous prime is 21089. The next prime is 21101. The reversal of 21100 is 112.

It is a Harshad number since it is a multiple of its sum of digits (4).

It is a nialpdrome in base 10.

It is a self number, because there is not a number n which added to its sum of digits gives 21100.

It is not an unprimeable number, because it can be changed into a prime (21101) 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 5 ways as a sum of consecutive naturals, for example, 6 + ... + 205.

2²¹¹⁰⁰ is an apocalyptic number.

21100 is a gapful number since it is divisible by the number (20) 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 21100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23002).

21100 is an abundant number, since it is smaller than the sum of its proper divisors (24904).

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

21100 is a wasteful number, since it uses less digits than its factorization.

21100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 225 (or 218 counting only the distinct ones).

The product of its (nonzero) digits is 2, while the sum is 4.

The square root of 21100 is about 145.2583904633. The cubic root of 21100 is about 27.6329648825.

Adding to 21100 its reverse (112), we get a palindrome (21212).

It can be divided in two parts, 21 and 100, that added together give a palindrome (121).

The spelling of 21100 in words is "twenty-one thousand, one hundred", and thus it is an iban number.