6661221666 has 64 divisors (see below), whose sum is σ = 15712081920. Its totient is φ = 1860615360.

The previous prime is 6661221653. The next prime is 6661221683.

It is a happy number.

6661221666 is nontrivially palindromic in base 10.

It is a nude number because it is divisible by every one of its digits.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 25386 + ... + 118181.

It is an arithmetic number, because the mean of its divisors is an integer number (245501280).

Almost surely, 2^6661221666 is an apocalyptic number.

6661221666 is a gapful number since it is divisible by the number (66) formed by its first and last digit.

6661221666 is an abundant number, since it is smaller than the sum of its proper divisors (9050860254).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

6661221666 is a wasteful number, since it uses less digits than its factorization.

6661221666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 143639.

The product of its digits is 186624, while the sum is 42.

The square root of 6661221666 is about 81616.3075984205. The cubic root of 6661221666 is about 1881.5595240189.

The spelling of 6661221666 in words is "six billion, six hundred sixty-one million, two hundred twenty-one thousand, six hundred sixty-six".