91591781 has 2 divisors, whose sum is σ = 91591782. Its totient is φ = 91591780.

The previous prime is 91591757. The next prime is 91591807. The reversal of 91591781 is 18719519.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 88529281 + 3062500 = 9409^2 + 1750^2 .

It is a cyclic number.

It is not a de Polignac number, because 91591781 - 2²⁶ = 24482917 is a prime.

It is a super-2 number, since 2×91591781² = 16778108693503922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91591711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45795890 + 45795891.

It is an arithmetic number, because the mean of its divisors is an integer number (45795891).

Almost surely, 2^91591781 is an apocalyptic number.

It is an amenable number.

91591781 is a deficient number, since it is larger than the sum of its proper divisors (1).

91591781 is an equidigital number, since it uses as much as digits as its factorization.

91591781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 22680, while the sum is 41.

The square root of 91591781 is about 9570.3595021295. The cubic root of 91591781 is about 450.7670555449.

The spelling of 91591781 in words is "ninety-one million, five hundred ninety-one thousand, seven hundred eighty-one".