21840400 has 30 divisors (see below), whose sum is σ = 52472522. Its totient is φ = 8736000.

The previous prime is 21840391. The next prime is 21840407. The reversal of 21840400 is 404812.

It can be written as a sum of positive squares in 3 ways, for example, as 50176 + 21790224 = 224^2 + 4668^2 .

It is not an unprimeable number, because it can be changed into a prime (21840407) 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, 26901 + ... + 27700.

Almost surely, 2^21840400 is an apocalyptic number.

21840400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21840400 is an abundant number, since it is smaller than the sum of its proper divisors (30632122).

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

21840400 is a wasteful number, since it uses less digits than its factorization.

21840400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54619 (or 54608 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 19.

The square root of 21840400 is about 4673.3713740725. The cubic root of 21840400 is about 279.5247038519.

The spelling of 21840400 in words is "twenty-one million, eight hundred forty thousand, four hundred".