21240405 has 24 divisors (see below), whose sum is σ = 37814712. Its totient is φ = 11021184.

The previous prime is 21240403. The next prime is 21240433. The reversal of 21240405 is 50404212.

21240405 is a `hidden beast` number, since 21 + 240 + 405 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 6563844 + 14676561 = 2562^2 + 3831^2 .

It is not a de Polignac number, because 21240405 - 2¹ = 21240403 is a prime.

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 23 ways as a sum of consecutive naturals, for example, 4714 + ... + 8043.

It is an arithmetic number, because the mean of its divisors is an integer number (1575613).

Almost surely, 2^21240405 is an apocalyptic number.

It is an amenable number.

21240405 is a deficient number, since it is larger than the sum of its proper divisors (16574307).

21240405 is a wasteful number, since it uses less digits than its factorization.

21240405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12805 (or 12802 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21240405 is about 4608.7313872692. The cubic root of 21240405 is about 276.9412179177.

Adding to 21240405 its reverse (50404212), we get a palindrome (71644617).

The spelling of 21240405 in words is "twenty-one million, two hundred forty thousand, four hundred five".