20666 has 4 divisors (see below), whose sum is σ = 31002. Its totient is φ = 10332.

The previous prime is 20663. The next prime is 20681. The reversal of 20666 is 66602.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 66602 = 2 ⋅33301.

It can be written as a sum of positive squares in only one way, i.e., 15625 + 5041 = 125^2 + 71^2 .

20666 is a modest number, since divided by 666 gives 20 as remainder.

It is a Curzon number.

It is a plaindrome in base 11.

It is a nialpdrome in base 12 and base 14.

It is not an unprimeable number, because it can be changed into a prime (20663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5165 + ... + 5168.

2²⁰⁶⁶⁶ is an apocalyptic number.

20666 is a deficient number, since it is larger than the sum of its proper divisors (10336).

20666 is a wasteful number, since it uses less digits than its factorization.

20666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10335.

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 20666 is about 143.7567389725. The cubic root of 20666 is about 27.4421926186.

It can be divided in two parts, 206 and 66, that added together give a palindrome (272).

The spelling of 20666 in words is "twenty thousand, six hundred sixty-six".