991109909 has 2 divisors, whose sum is σ = 991109910. Its totient is φ = 991109908.

The previous prime is 991109891. The next prime is 991109969. The reversal of 991109909 is 909901199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 830707684 + 160402225 = 28822^2 + 12665^2 .

It is a cyclic number.

It is not a de Polignac number, because 991109909 - 2²⁰ = 990061333 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991109969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495554954 + 495554955.

It is an arithmetic number, because the mean of its divisors is an integer number (495554955).

Almost surely, 2^991109909 is an apocalyptic number.

It is an amenable number.

991109909 is a deficient number, since it is larger than the sum of its proper divisors (1).

991109909 is an equidigital number, since it uses as much as digits as its factorization.

991109909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 59049, while the sum is 47.

The square root of 991109909 is about 31481.8981162191. The cubic root of 991109909 is about 997.0278111790.

The spelling of 991109909 in words is "nine hundred ninety-one million, one hundred nine thousand, nine hundred nine".