21240388 has 12 divisors (see below), whose sum is σ = 40030060. Its totient is φ = 9803232.

The previous prime is 21240379. The next prime is 21240389. The reversal of 21240388 is 88304212.

It can be written as a sum of positive squares in 2 ways, for example, as 3415104 + 17825284 = 1848^2 + 4222^2 .

It is not an unprimeable number, because it can be changed into a prime (21240389) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 204183 + ... + 204286.

Almost surely, 2^21240388 is an apocalyptic number.

It is an amenable number.

21240388 is a deficient number, since it is larger than the sum of its proper divisors (18789672).

21240388 is a wasteful number, since it uses less digits than its factorization.

21240388 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 408486 (or 408484 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 28.

The square root of 21240388 is about 4608.7295429435. The cubic root of 21240388 is about 276.9411440333.

The spelling of 21240388 in words is "twenty-one million, two hundred forty thousand, three hundred eighty-eight".