20665591 has 4 divisors (see below), whose sum is σ = 21881232. Its totient is φ = 19449952.

The previous prime is 20665577. The next prime is 20665621. The reversal of 20665591 is 19556602.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 20665591 - 2¹¹ = 20663543 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 (20665501) 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, 607795 + ... + 607828.

It is an arithmetic number, because the mean of its divisors is an integer number (5470308).

Almost surely, 2^20665591 is an apocalyptic number.

20665591 is a deficient number, since it is larger than the sum of its proper divisors (1215641).

20665591 is a wasteful number, since it uses less digits than its factorization.

20665591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1215640.

The product of its (nonzero) digits is 16200, while the sum is 34.

The square root of 20665591 is about 4545.9422565624. The cubic root of 20665591 is about 274.4201158163.

The spelling of 20665591 in words is "twenty million, six hundred sixty-five thousand, five hundred ninety-one".