991868809 has 2 divisors, whose sum is σ = 991868810. Its totient is φ = 991868808.

The previous prime is 991868789. The next prime is 991868821. The reversal of 991868809 is 908868199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 961310025 + 30558784 = 31005^2 + 5528^2 .

It is a cyclic number.

It is not a de Polignac number, because 991868809 - 2¹¹ = 991866761 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (991868209) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495934404 + 495934405.

It is an arithmetic number, because the mean of its divisors is an integer number (495934405).

Almost surely, 2^991868809 is an apocalyptic number.

It is an amenable number.

991868809 is a deficient number, since it is larger than the sum of its proper divisors (1).

991868809 is an equidigital number, since it uses as much as digits as its factorization.

991868809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2239488, while the sum is 58.

The square root of 991868809 is about 31493.9487679776. The cubic root of 991868809 is about 997.2822233817.

The spelling of 991868809 in words is "nine hundred ninety-one million, eight hundred sixty-eight thousand, eight hundred nine".