21660400 has 30 divisors (see below), whose sum is σ = 52040072. Its totient is φ = 8664000.

The previous prime is 21660389. The next prime is 21660407. The reversal of 21660400 is 406612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660407) 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, 26676 + ... + 27475.

Almost surely, 2^21660400 is an apocalyptic number.

21660400 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21660400 is an abundant number, since it is smaller than the sum of its proper divisors (30379672).

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

21660400 is a wasteful number, since it uses less digits than its factorization.

21660400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54169 (or 54158 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 19.

The square root of 21660400 is about 4654.0734845939. The cubic root of 21660400 is about 278.7546735862.

The spelling of 21660400 in words is "twenty-one million, six hundred sixty thousand, four hundred".