21609791 has 4 divisors (see below), whose sum is σ = 24696912. Its totient is φ = 18522672.

The previous prime is 21609787. The next prime is 21609817. The reversal of 21609791 is 19790612.

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

It is not a de Polignac number, because 21609791 - 2² = 21609787 is a prime.

It is a Duffinian number.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21609701) 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, 1543550 + ... + 1543563.

It is an arithmetic number, because the mean of its divisors is an integer number (6174228).

Almost surely, 2^21609791 is an apocalyptic number.

21609791 is a deficient number, since it is larger than the sum of its proper divisors (3087121).

21609791 is an equidigital number, since it uses as much as digits as its factorization.

21609791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3087120.

The product of its (nonzero) digits is 6804, while the sum is 35.

The square root of 21609791 is about 4648.6332399965. The cubic root of 21609791 is about 278.5374031013.

The spelling of 21609791 in words is "twenty-one million, six hundred nine thousand, seven hundred ninety-one".