21102400 has 126 divisors (see below), whose sum is σ = 57598310. Its totient is φ = 7603200.

The previous prime is 21102391. The next prime is 21102409. The reversal of 21102400 is 420112.

It is an interprime number because it is at equal distance from previous prime (21102391) and next prime (21102409).

It can be written as a sum of positive squares in 3 ways, for example, as 2509056 + 18593344 = 1584^2 + 4312^2 .

It is a super-2 number, since 2×21102400² = 890622571520000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21102409) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 193546 + ... + 193654.

Almost surely, 2^21102400 is an apocalyptic number.

21102400 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 21102400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28799155).

21102400 is an abundant number, since it is smaller than the sum of its proper divisors (36495910).

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

21102400 is a wasteful number, since it uses less digits than its factorization.

21102400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 153 (or 127 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 10.

The square root of 21102400 is about 4593.7348639206. The cubic root of 21102400 is about 276.3401253818.

Adding to 21102400 its reverse (420112), we get a palindrome (21522512).

The spelling of 21102400 in words is "twenty-one million, one hundred two thousand, four hundred".