91781857 has 2 divisors, whose sum is σ = 91781858. Its totient is φ = 91781856.

The previous prime is 91781819. The next prime is 91781869. The reversal of 91781857 is 75818719.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76108176 + 15673681 = 8724^2 + 3959^2 .

It is an emirp because it is prime and its reverse (75818719) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-91781857 is a prime.

It is not a weakly prime, because it can be changed into another prime (91781887) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45890928 + 45890929.

It is an arithmetic number, because the mean of its divisors is an integer number (45890929).

Almost surely, 2^91781857 is an apocalyptic number.

It is an amenable number.

91781857 is a deficient number, since it is larger than the sum of its proper divisors (1).

91781857 is an equidigital number, since it uses as much as digits as its factorization.

91781857 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 141120, while the sum is 46.

The square root of 91781857 is about 9580.2848078750. The cubic root of 91781857 is about 451.0786584600.

The spelling of 91781857 in words is "ninety-one million, seven hundred eighty-one thousand, eight hundred fifty-seven".