21666816669 has 4 divisors (see below), whose sum is σ = 28889088896. Its totient is φ = 14444544444.

The previous prime is 21666816617. The next prime is 21666816781. The reversal of 21666816669 is 96661866612.

It is a happy number.

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.

It is not a de Polignac number, because 21666816669 - 2¹³ = 21666808477 is a prime.

It is a super-2 number, since 2×21666816669² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666816169) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3611136109 + ... + 3611136114.

It is an arithmetic number, because the mean of its divisors is an integer number (7222272224).

Almost surely, 2^21666816669 is an apocalyptic number.

It is an amenable number.

21666816669 is a deficient number, since it is larger than the sum of its proper divisors (7222272227).

21666816669 is an equidigital number, since it uses as much as digits as its factorization.

21666816669 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7222272226.

The product of its digits is 6718464, while the sum is 57.

The spelling of 21666816669 in words is "twenty-one billion, six hundred sixty-six million, eight hundred sixteen thousand, six hundred sixty-nine".