21605717 has 24 divisors (see below), whose sum is σ = 27633600. Its totient is φ = 16765056.

The previous prime is 21605711. The next prime is 21605747. The reversal of 21605717 is 71750612.

It is not a de Polignac number, because 21605717 - 2⁸ = 21605461 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21605717.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605711) 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 23 ways as a sum of consecutive naturals, for example, 20909 + ... + 21917.

It is an arithmetic number, because the mean of its divisors is an integer number (1151400).

Almost surely, 2^21605717 is an apocalyptic number.

It is an amenable number.

21605717 is a deficient number, since it is larger than the sum of its proper divisors (6027883).

21605717 is a wasteful number, since it uses less digits than its factorization.

21605717 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1065 (or 1058 counting only the distinct ones).

The product of its (nonzero) digits is 2940, while the sum is 29.

The square root of 21605717 is about 4648.1950260289. The cubic root of 21605717 is about 278.5198981858.

It can be divided in two parts, 21605 and 717, that added together give a palindrome (22322).

The spelling of 21605717 in words is "twenty-one million, six hundred five thousand, seven hundred seventeen".