21504400 has 60 divisors (see below), whose sum is σ = 53097172. Its totient is φ = 8363520.

The previous prime is 21504397. The next prime is 21504403. The reversal of 21504400 is 440512.

It is an interprime number because it is at equal distance from previous prime (21504397) and next prime (21504403).

It can be written as a sum of positive squares in 6 ways, for example, as 3254416 + 18249984 = 1804^2 + 4272^2 .

It is a Harshad number since it is a multiple of its sum of digits (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21504403) 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 11 ways as a sum of consecutive naturals, for example, 14074 + ... + 15526.

Almost surely, 2^21504400 is an apocalyptic number.

21504400 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 21504400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26548586).

21504400 is an abundant number, since it is smaller than the sum of its proper divisors (31592772).

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

21504400 is a wasteful number, since it uses less digits than its factorization.

21504400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1508 (or 1497 counting only the distinct ones).

The product of its (nonzero) digits is 160, while the sum is 16.

The square root of 21504400 is about 4637.2836876775. The cubic root of 21504400 is about 278.0838557998.

Adding to 21504400 its reverse (440512), we get a palindrome (21944912).

It can be divided in two parts, 21504 and 400, that added together give a square (21904 = 148²).

The spelling of 21504400 in words is "twenty-one million, five hundred four thousand, four hundred".