21605617 has 8 divisors (see below), whose sum is σ = 23804352. Its totient is φ = 19446000.

The previous prime is 21605611. The next prime is 21605627. The reversal of 21605617 is 71650612.

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 21605617 - 2¹⁵ = 21572849 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21605611) 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 7 ways as a sum of consecutive naturals, for example, 8613 + ... + 10834.

It is an arithmetic number, because the mean of its divisors is an integer number (2975544).

Almost surely, 2^21605617 is an apocalyptic number.

It is an amenable number.

21605617 is a deficient number, since it is larger than the sum of its proper divisors (2198735).

21605617 is a wasteful number, since it uses less digits than its factorization.

21605617 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19559.

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21605617 is about 4648.1842691528. The cubic root of 21605617 is about 278.5194684842.

It can be divided in two parts, 21605 and 617, that added together give a palindrome (22222).

The spelling of 21605617 in words is "twenty-one million, six hundred five thousand, six hundred seventeen".