9991891901 has 2 divisors, whose sum is σ = 9991891902. Its totient is φ = 9991891900.

The previous prime is 9991891891. The next prime is 9991891937. The reversal of 9991891901 is 1091981999.

9991891901 is digitally balanced in base 2 and base 3, because in such bases it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6827716900 + 3164175001 = 82630^2 + 56251^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-9991891901 is a prime.

It is a super-2 number, since 2×9991891901² (a number of 21 digits) contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9991891001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4995945950 + 4995945951.

It is an arithmetic number, because the mean of its divisors is an integer number (4995945951).

Almost surely, 2^9991891901 is an apocalyptic number.

It is an amenable number.

9991891901 is a deficient number, since it is larger than the sum of its proper divisors (1).

9991891901 is an equidigital number, since it uses as much as digits as its factorization.

9991891901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 472392, while the sum is 56.

The square root of 9991891901 is about 99959.4512840082. The cubic root of 9991891901 is about 2153.8522535966.

The spelling of 9991891901 in words is "nine billion, nine hundred ninety-one million, eight hundred ninety-one thousand, nine hundred one".