21100400 has 120 divisors (see below), whose sum is σ = 56045520. Its totient is φ = 7598080.

The previous prime is 21100399. The next prime is 21100403. The reversal of 21100400 is 400112.

It is a Harshad number since it is a multiple of its sum of digits (8).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21100403) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 197147 + ... + 197253.

It is an arithmetic number, because the mean of its divisors is an integer number (467046).

Almost surely, 2^21100400 is an apocalyptic number.

21100400 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 21100400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28022760).

21100400 is an abundant number, since it is smaller than the sum of its proper divisors (34945120).

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

21100400 is a wasteful number, since it uses less digits than its factorization.

21100400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171 (or 160 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 8.

The square root of 21100400 is about 4593.5171709704. The cubic root of 21100400 is about 276.3313949733.

Adding to 21100400 its reverse (400112), we get a palindrome (21500512).

The spelling of 21100400 in words is "twenty-one million, one hundred thousand, four hundred".