21408305 has 8 divisors (see below), whose sum is σ = 25878312. Its totient is φ = 17001088.

The previous prime is 21408301. The next prime is 21408319. The reversal of 21408305 is 50380412.

It can be written as a sum of positive squares in 4 ways, for example, as 3625216 + 17783089 = 1904^2 + 4217^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21408305 - 2² = 21408301 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21408301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14942 + ... + 16311.

It is an arithmetic number, because the mean of its divisors is an integer number (3234789).

Almost surely, 2^21408305 is an apocalyptic number.

It is an amenable number.

21408305 is a deficient number, since it is larger than the sum of its proper divisors (4470007).

21408305 is a wasteful number, since it uses less digits than its factorization.

21408305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31395.

The product of its (nonzero) digits is 960, while the sum is 23.

The square root of 21408305 is about 4626.9109565670. The cubic root of 21408305 is about 277.6690202092.

Adding to 21408305 its reverse (50380412), we get a palindrome (71788717).

The spelling of 21408305 in words is "twenty-one million, four hundred eight thousand, three hundred five".