91081981 has 2 divisors, whose sum is σ = 91081982. Its totient is φ = 91081980.

The previous prime is 91081943. The next prime is 91081993. The reversal of 91081981 is 18918019.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80460900 + 10621081 = 8970^2 + 3259^2 .

It is an emirp because it is prime and its reverse (18918019) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91081981 - 2⁹ = 91081469 is a prime.

It is a super-2 number, since 2×91081981² = 16591854525768722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 91081981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (91081481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45540990 + 45540991.

It is an arithmetic number, because the mean of its divisors is an integer number (45540991).

Almost surely, 2^91081981 is an apocalyptic number.

It is an amenable number.

91081981 is a deficient number, since it is larger than the sum of its proper divisors (1).

91081981 is an equidigital number, since it uses as much as digits as its factorization.

91081981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 37.

The square root of 91081981 is about 9543.6880187902. The cubic root of 91081981 is about 449.9291756850.

The spelling of 91081981 in words is "ninety-one million, eighty-one thousand, nine hundred eighty-one".