991908393569 has 2 divisors, whose sum is σ = 991908393570. Its totient is φ = 991908393568.

The previous prime is 991908393559. The next prime is 991908393611. The reversal of 991908393569 is 965393809199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 586852519969 + 405055873600 = 766063^2 + 636440^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991908393569 is a prime.

It is a super-2 number, since 2×991908393569² (a number of 25 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (991908393559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495954196784 + 495954196785.

It is an arithmetic number, because the mean of its divisors is an integer number (495954196785).

Almost surely, 2^991908393569 is an apocalyptic number.

It is an amenable number.

991908393569 is a deficient number, since it is larger than the sum of its proper divisors (1).

991908393569 is an equidigital number, since it uses as much as digits as its factorization.

991908393569 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 127545840, while the sum is 71.

The spelling of 991908393569 in words is "nine hundred ninety-one billion, nine hundred eight million, three hundred ninety-three thousand, five hundred sixty-nine".