21240400 has 30 divisors (see below), whose sum is σ = 51031022. Its totient is φ = 8496000.

The previous prime is 21240391. The next prime is 21240403. The reversal of 21240400 is 404212.

It can be written as a sum of positive squares in 3 ways, for example, as 3968064 + 17272336 = 1992^2 + 4156^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21240403) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 26151 + ... + 26950.

Almost surely, 2^21240400 is an apocalyptic number.

21240400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21240400 is an abundant number, since it is smaller than the sum of its proper divisors (29790622).

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

21240400 is a wasteful number, since it uses less digits than its factorization.

21240400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53119 (or 53108 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 13.

The square root of 21240400 is about 4608.7308448205. The cubic root of 21240400 is about 276.9411961870.

Adding to 21240400 its reverse (404212), we get a palindrome (21644612).

The spelling of 21240400 in words is "twenty-one million, two hundred forty thousand, four hundred".