91009 has 2 divisors, whose sum is σ = 91010. Its totient is φ = 91008.

The previous prime is 90997. The next prime is 91019. The reversal of 91009 is 90019.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 67600 + 23409 = 260^2 + 153^2 .

It is an emirp because it is prime and its reverse (90019) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91009 - 2⁵ = 90977 is a prime.

It is equal to p₈₈₀₃ and since 91009 and 8803 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (91019) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45504 + 45505.

It is an arithmetic number, because the mean of its divisors is an integer number (45505).

2⁹¹⁰⁰⁹ is an apocalyptic number.

It is an amenable number.

91009 is a deficient number, since it is larger than the sum of its proper divisors (1).

91009 is an equidigital number, since it uses as much as digits as its factorization.

91009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 81, while the sum is 19.

The square root of 91009 is about 301.6769795659. The cubic root of 91009 is about 44.9808972417.

Subtracting from 91009 its reverse (90019), we obtain a triangular number (990 = T₄₄).

The spelling of 91009 in words is "ninety-one thousand, nine".