81185891 has 2 divisors, whose sum is σ = 81185892. Its totient is φ = 81185890.

The previous prime is 81185857. The next prime is 81185903. The reversal of 81185891 is 19858118.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81185891 - 2¹⁰ = 81184867 is a prime.

It is a super-2 number, since 2×81185891² = 13182297794927762, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81185191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40592945 + 40592946.

It is an arithmetic number, because the mean of its divisors is an integer number (40592946).

Almost surely, 2^81185891 is an apocalyptic number.

81185891 is a deficient number, since it is larger than the sum of its proper divisors (1).

81185891 is an equidigital number, since it uses as much as digits as its factorization.

81185891 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 81185891 is about 9010.3213594189. The cubic root of 81185891 is about 433.0056073675.

The spelling of 81185891 in words is "eighty-one million, one hundred eighty-five thousand, eight hundred ninety-one".