21309617 has 16 divisors (see below), whose sum is σ = 25300992. Its totient is φ = 17562960.

The previous prime is 21309611. The next prime is 21309623. The reversal of 21309617 is 71690312.

21309617 is nontrivially palindromic in base 13.

It is an interprime number because it is at equal distance from previous prime (21309611) and next prime (21309623).

It is a cyclic number.

It is not a de Polignac number, because 21309617 - 2⁴ = 21309601 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21309617.

It is not an unprimeable number, because it can be changed into a prime (21309611) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 61238 + ... + 61584.

It is an arithmetic number, because the mean of its divisors is an integer number (1581312).

Almost surely, 2^21309617 is an apocalyptic number.

It is an amenable number.

21309617 is a deficient number, since it is larger than the sum of its proper divisors (3991375).

21309617 is a wasteful number, since it uses less digits than its factorization.

21309617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 668.

The product of its (nonzero) digits is 2268, while the sum is 29.

The square root of 21309617 is about 4616.2340711883. The cubic root of 21309617 is about 277.2416967123.

Adding to 21309617 its reverse (71690312), we get a palindrome (92999929).

The spelling of 21309617 in words is "twenty-one million, three hundred nine thousand, six hundred seventeen".