81985181 has 2 divisors, whose sum is σ = 81985182. Its totient is φ = 81985180.

The previous prime is 81985177. The next prime is 81985187. The reversal of 81985181 is 18158918.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 73188025 + 8797156 = 8555^2 + 2966^2 .

It is a cyclic number.

It is not a de Polignac number, because 81985181 - 2² = 81985177 is a prime.

It is a super-2 number, since 2×81985181² = 13443139807205522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81985187) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40992590 + 40992591.

It is an arithmetic number, because the mean of its divisors is an integer number (40992591).

Almost surely, 2^81985181 is an apocalyptic number.

It is an amenable number.

81985181 is a deficient number, since it is larger than the sum of its proper divisors (1).

81985181 is an equidigital number, since it uses as much as digits as its factorization.

81985181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23040, while the sum is 41.

The square root of 81985181 is about 9054.5668587735. The cubic root of 81985181 is about 434.4219759143.

The spelling of 81985181 in words is "eighty-one million, nine hundred eighty-five thousand, one hundred eighty-one".