21012405 has 16 divisors (see below), whose sum is σ = 33846144. Its totient is φ = 11131200.

The previous prime is 21012401. The next prime is 21012413. The reversal of 21012405 is 50421012.

It is not a de Polignac number, because 21012405 - 2² = 21012401 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21012401) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2374 + ... + 6903.

It is an arithmetic number, because the mean of its divisors is an integer number (2115384).

Almost surely, 2^21012405 is an apocalyptic number.

It is an amenable number.

21012405 is a deficient number, since it is larger than the sum of its proper divisors (12833739).

21012405 is a wasteful number, since it uses less digits than its factorization.

21012405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9436.

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21012405 is about 4583.9289915966. The cubic root of 21012405 is about 275.9467314757.

Adding to 21012405 its reverse (50421012), we get a palindrome (71433417).

The spelling of 21012405 in words is "twenty-one million, twelve thousand, four hundred five".