21688117 has 4 divisors (see below), whose sum is σ = 23659776. Its totient is φ = 19716460.

The previous prime is 21688111. The next prime is 21688159. The reversal of 21688117 is 71188612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21688117 - 2³ = 21688109 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688111) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 985813 + ... + 985834.

It is an arithmetic number, because the mean of its divisors is an integer number (5914944).

Almost surely, 2^21688117 is an apocalyptic number.

It is an amenable number.

21688117 is a deficient number, since it is larger than the sum of its proper divisors (1971659).

21688117 is a wasteful number, since it uses less digits than its factorization.

21688117 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1971658.

The product of its digits is 5376, while the sum is 34.

The square root of 21688117 is about 4657.0502466690. The cubic root of 21688117 is about 278.8735225777.

The spelling of 21688117 in words is "twenty-one million, six hundred eighty-eight thousand, one hundred seventeen".