21305605 has 8 divisors (see below), whose sum is σ = 25674264. Its totient is φ = 16972800.

The previous prime is 21305569. The next prime is 21305611. The reversal of 21305605 is 50650312.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 2313441 + 18992164 = 1521^2 + 4358^2 .

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

It is a de Polignac number, because none of the positive numbers 2^k-21305605 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7636 + ... + 10045.

It is an arithmetic number, because the mean of its divisors is an integer number (3209283).

Almost surely, 2^21305605 is an apocalyptic number.

It is an amenable number.

21305605 is a deficient number, since it is larger than the sum of its proper divisors (4368659).

21305605 is a wasteful number, since it uses less digits than its factorization.

21305605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17927.

The product of its (nonzero) digits is 900, while the sum is 22.

The square root of 21305605 is about 4615.7994973785. The cubic root of 21305605 is about 277.2242966889.

Adding to 21305605 its reverse (50650312), we get a palindrome (71955917).

The spelling of 21305605 in words is "twenty-one million, three hundred five thousand, six hundred five".