8991661997 has 4 divisors (see below), whose sum is σ = 9002154876. Its totient is φ = 8981169120.

The previous prime is 8991661993. The next prime is 8991662039. The reversal of 8991661997 is 7991661998.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 7991661998 = 2 ⋅3995830999.

It can be written as a sum of positive squares in 2 ways, for example, as 8800503721 + 191158276 = 93811^2 + 13826^2 .

It is a cyclic number.

It is not a de Polignac number, because 8991661997 - 2² = 8991661993 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8991661993) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5245154 + ... + 5246867.

It is an arithmetic number, because the mean of its divisors is an integer number (2250538719).

Almost surely, 2^8991661997 is an apocalyptic number.

It is an amenable number.

8991661997 is a deficient number, since it is larger than the sum of its proper divisors (10492879).

8991661997 is a wasteful number, since it uses less digits than its factorization.

8991661997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10492878.

The product of its digits is 13226976, while the sum is 65.

The square root of 8991661997 is about 94824.3744877866. The cubic root of 8991661997 is about 2079.4412636474.

Subtracting from 8991661997 its reverse (7991661998), we obtain a palindrome (999999999).

The spelling of 8991661997 in words is "eight billion, nine hundred ninety-one million, six hundred sixty-one thousand, nine hundred ninety-seven".