9991111666 has 4 divisors (see below), whose sum is σ = 14986667502. Its totient is φ = 4995555832.

The previous prime is 9991111643. The next prime is 9991111679. The reversal of 9991111666 is 6661111999.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 6661111999 = 2753 ⋅2419583.

It can be written as a sum of positive squares in only one way, i.e., 9671739025 + 319372641 = 98345^2 + 17871^2 .

9991111666 is a strobogrammatic number because it is the same when read upside-down.

It is a zygodrome in base 10.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2497777915 + ... + 2497777918.

Almost surely, 2^9991111666 is an apocalyptic number.

9991111666 is a deficient number, since it is larger than the sum of its proper divisors (4995555836).

9991111666 is a wasteful number, since it uses less digits than its factorization.

9991111666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4995555835.

The product of its digits is 157464, while the sum is 49.

The square root of 9991111666 is about 99955.5484502986. The cubic root of 9991111666 is about 2153.7961896508.

The spelling of 9991111666 in words is "nine billion, nine hundred ninety-one million, one hundred eleven thousand, six hundred sixty-six".