21605705 has 8 divisors (see below), whose sum is σ = 28283904. Its totient is φ = 15713200.

The previous prime is 21605693. The next prime is 21605711. The reversal of 21605705 is 50750612.

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

It is not a de Polignac number, because 21605705 - 2²⁰ = 20557129 is a prime.

It is a zygodrome in base 3.

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, 196361 + ... + 196470.

It is an arithmetic number, because the mean of its divisors is an integer number (3535488).

Almost surely, 2^21605705 is an apocalyptic number.

It is an amenable number.

21605705 is a deficient number, since it is larger than the sum of its proper divisors (6678199).

21605705 is a wasteful number, since it uses less digits than its factorization.

21605705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 392847.

The product of its (nonzero) digits is 2100, while the sum is 26.

The square root of 21605705 is about 4648.1937352051. The cubic root of 21605705 is about 278.5198466217.

The spelling of 21605705 in words is "twenty-one million, six hundred five thousand, seven hundred five".