991901 has 2 divisors, whose sum is σ = 991902. Its totient is φ = 991900.

The previous prime is 991889. The next prime is 991909. The reversal of 991901 is 109199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 902500 + 89401 = 950^2 + 299^2 .

It is an emirp because it is prime and its reverse (109199) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-991901 is a prime.

It is a Chen prime.

It is equal to p₇₇₉₁₅ and since 991901 and 77915 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495950 + 495951.

It is an arithmetic number, because the mean of its divisors is an integer number (495951).

2⁹⁹¹⁹⁰¹ is an apocalyptic number.

It is an amenable number.

991901 is a deficient number, since it is larger than the sum of its proper divisors (1).

991901 is an equidigital number, since it uses as much as digits as its factorization.

991901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 729, while the sum is 29.

The square root of 991901 is about 995.9422674031. The cubic root of 991901 is about 99.7293012162.

The spelling of 991901 in words is "nine hundred ninety-one thousand, nine hundred one".