21686191 has 4 divisors (see below), whose sum is σ = 21768912. Its totient is φ = 21603472.

The previous prime is 21686177. The next prime is 21686207. The reversal of 21686191 is 19168612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21686191 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 (21686111) 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, 40966 + ... + 41491.

It is an arithmetic number, because the mean of its divisors is an integer number (5442228).

Almost surely, 2^21686191 is an apocalyptic number.

21686191 is a deficient number, since it is larger than the sum of its proper divisors (82721).

21686191 is an equidigital number, since it uses as much as digits as its factorization.

21686191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82720.

The product of its digits is 5184, while the sum is 34.

The square root of 21686191 is about 4656.8434588249. The cubic root of 21686191 is about 278.8652672690.

The spelling of 21686191 in words is "twenty-one million, six hundred eighty-six thousand, one hundred ninety-one".