21042405 has 24 divisors (see below), whose sum is σ = 38394720. Its totient is φ = 10631520.

The previous prime is 21042383. The next prime is 21042407. The reversal of 21042405 is 50424012.

It is not a de Polignac number, because 21042405 - 2¹⁰ = 21041381 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21042407) 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, 11451 + ... + 13160.

It is an arithmetic number, because the mean of its divisors is an integer number (1599780).

Almost surely, 2^21042405 is an apocalyptic number.

It is an amenable number.

21042405 is a deficient number, since it is larger than the sum of its proper divisors (17352315).

21042405 is a wasteful number, since it uses less digits than its factorization.

21042405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24641 (or 24638 counting only the distinct ones).

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

The square root of 21042405 is about 4587.2001264388. The cubic root of 21042405 is about 276.0779946556.

Adding to 21042405 its reverse (50424012), we get a palindrome (71466417).

The spelling of 21042405 in words is "twenty-one million, forty-two thousand, four hundred five".