91981217 has 2 divisors, whose sum is σ = 91981218. Its totient is φ = 91981216.

The previous prime is 91981213. The next prime is 91981231. The reversal of 91981217 is 71218919.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 90706576 + 1274641 = 9524^2 + 1129^2 .

It is a cyclic number.

It is not a de Polignac number, because 91981217 - 2² = 91981213 is a prime.

It is not a weakly prime, because it can be changed into another prime (91981213) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45990608 + 45990609.

It is an arithmetic number, because the mean of its divisors is an integer number (45990609).

Almost surely, 2^91981217 is an apocalyptic number.

It is an amenable number.

91981217 is a deficient number, since it is larger than the sum of its proper divisors (1).

91981217 is an equidigital number, since it uses as much as digits as its factorization.

91981217 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9072, while the sum is 38.

The square root of 91981217 is about 9590.6838650849. The cubic root of 91981217 is about 451.4050192913.

The spelling of 91981217 in words is "ninety-one million, nine hundred eighty-one thousand, two hundred seventeen".