6661991666 has 16 divisors (see below), whose sum is σ = 10906429248. Its totient is φ = 3026792400.

The previous prime is 6661991663. The next prime is 6661991669.

6661991666 is nontrivially palindromic in base 10.

It is an interprime number because it is at equal distance from previous prime (6661991663) and next prime (6661991669).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (6661991663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19310 + ... + 117033.

It is an arithmetic number, because the mean of its divisors is an integer number (681651828).

Almost surely, 2^6661991666 is an apocalyptic number.

6661991666 is a deficient number, since it is larger than the sum of its proper divisors (4244437582).

6661991666 is a wasteful number, since it uses less digits than its factorization.

6661991666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 138577.

The product of its digits is 3779136, while the sum is 56.

The square root of 6661991666 is about 81621.0246566410. The cubic root of 6661991666 is about 1881.6320204811.

The spelling of 6661991666 in words is "six billion, six hundred sixty-one million, nine hundred ninety-one thousand, six hundred sixty-six".