81859181 has 2 divisors, whose sum is σ = 81859182. Its totient is φ = 81859180.

The previous prime is 81859177. The next prime is 81859291. The reversal of 81859181 is 18195818.

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., 72829156 + 9030025 = 8534^2 + 3005^2 .

It is a cyclic number.

It is not a de Polignac number, because 81859181 - 2² = 81859177 is a prime.

It is a super-2 number, since 2×81859181² = 13401851027981522, 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 (81859111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40929590 + 40929591.

It is an arithmetic number, because the mean of its divisors is an integer number (40929591).

Almost surely, 2^81859181 is an apocalyptic number.

It is an amenable number.

81859181 is a deficient number, since it is larger than the sum of its proper divisors (1).

81859181 is an equidigital number, since it uses as much as digits as its factorization.

81859181 is an evil number, because the sum of its binary digits is even.

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

The square root of 81859181 is about 9047.6063685375. The cubic root of 81859181 is about 434.1993127719.

The spelling of 81859181 in words is "eighty-one million, eight hundred fifty-nine thousand, one hundred eighty-one".