20660021 has 4 divisors (see below), whose sum is σ = 20670912. Its totient is φ = 20649132.

The previous prime is 20659999. The next prime is 20660047. The reversal of 20660021 is 12006602.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 20660021 - 2¹⁰ = 20658997 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 (20660051) 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, 1775 + ... + 6668.

It is an arithmetic number, because the mean of its divisors is an integer number (5167728).

Almost surely, 2^20660021 is an apocalyptic number.

It is an amenable number.

20660021 is a deficient number, since it is larger than the sum of its proper divisors (10891).

20660021 is an equidigital number, since it uses as much as digits as its factorization.

20660021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10890.

The product of its (nonzero) digits is 144, while the sum is 17.

The square root of 20660021 is about 4545.3295810095. The cubic root of 20660021 is about 274.3954587685.

Adding to 20660021 its reverse (12006602), we get a palindrome (32666623).

The spelling of 20660021 in words is "twenty million, six hundred sixty thousand, twenty-one".