21688791 has 8 divisors (see below), whose sum is σ = 29092224. Its totient is φ = 14372280.

The previous prime is 21688783. The next prime is 21688817. The reversal of 21688791 is 19788612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21688791 - 2³ = 21688783 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688721) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21145 + ... + 22146.

It is an arithmetic number, because the mean of its divisors is an integer number (3636528).

Almost surely, 2^21688791 is an apocalyptic number.

21688791 is a deficient number, since it is larger than the sum of its proper divisors (7403433).

21688791 is a wasteful number, since it uses less digits than its factorization.

21688791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43461.

The product of its digits is 48384, while the sum is 42.

The square root of 21688791 is about 4657.1226095090. The cubic root of 21688791 is about 278.8764113917.

The spelling of 21688791 in words is "twenty-one million, six hundred eighty-eight thousand, seven hundred ninety-one".