21306405 has 16 divisors (see below), whose sum is σ = 34151040. Its totient is φ = 11343168.

The previous prime is 21306359. The next prime is 21306407. The reversal of 21306405 is 50460312.

It is a happy number.

It is not a de Polignac number, because 21306405 - 2⁸ = 21306149 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21306407) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11739 + ... + 13431.

It is an arithmetic number, because the mean of its divisors is an integer number (2134440).

Almost surely, 2^21306405 is an apocalyptic number.

It is an amenable number.

21306405 is a deficient number, since it is larger than the sum of its proper divisors (12844635).

21306405 is a wasteful number, since it uses less digits than its factorization.

21306405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2540.

The product of its (nonzero) digits is 720, while the sum is 21.

The square root of 21306405 is about 4615.8861554419. The cubic root of 21306405 is about 277.2277664591.

Adding to 21306405 its reverse (50460312), we get a palindrome (71766717).

The spelling of 21306405 in words is "twenty-one million, three hundred six thousand, four hundred five".