91781 has 2 divisors, whose sum is σ = 91782. Its totient is φ = 91780.

The previous prime is 91771. The next prime is 91801. The reversal of 91781 is 18719.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 70756 + 21025 = 266^2 + 145^2 .

It is an emirp because it is prime and its reverse (18719) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-91781 is a prime.

It is a super-2 number, since 2×91781² = 16847503922, which contains 22 as substring.

It is a Chen prime.

It is a zygodrome in base 3.

It is a self number, because there is not a number n which added to its sum of digits gives 91781.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 91781.

It is not a weakly prime, because it can be changed into another prime (91711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45890 + 45891.

It is an arithmetic number, because the mean of its divisors is an integer number (45891).

2⁹¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

91781 is a deficient number, since it is larger than the sum of its proper divisors (1).

91781 is an equidigital number, since it uses as much as digits as its factorization.

91781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 504, while the sum is 26.

The square root of 91781 is about 302.9537918561. The cubic root of 91781 is about 45.1077254495.

The spelling of 91781 in words is "ninety-one thousand, seven hundred eighty-one".