9991661999 has 12 divisors (see below), whose sum is σ = 11066424600. Its totient is φ = 9013976400.

The previous prime is 9991661989. The next prime is 9991662007.

9991661999 is nontrivially palindromic in base 10.

It is a de Polignac number, because none of the positive numbers 2^k-9991661999 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9991661989) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 299324 + ... + 331025.

It is an arithmetic number, because the mean of its divisors is an integer number (922202050).

Almost surely, 2^9991661999 is an apocalyptic number.

9991661999 is a deficient number, since it is larger than the sum of its proper divisors (1074762601).

9991661999 is a wasteful number, since it uses less digits than its factorization.

9991661999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 630502 (or 630491 counting only the distinct ones).

The product of its digits is 19131876, while the sum is 68.

The square root of 9991661999 is about 99958.3013010925. The cubic root of 9991661999 is about 2153.8357342446.

The spelling of 9991661999 in words is "nine billion, nine hundred ninety-one million, six hundred sixty-one thousand, nine hundred ninety-nine".