81985889 has 2 divisors, whose sum is σ = 81985890. Its totient is φ = 81985888.

The previous prime is 81985879. The next prime is 81985913. The reversal of 81985889 is 98858918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 73960000 + 8025889 = 8600^2 + 2833^2 .

It is a cyclic number.

It is not a de Polignac number, because 81985889 - 2⁴ = 81985873 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81985819) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40992944 + 40992945.

It is an arithmetic number, because the mean of its divisors is an integer number (40992945).

Almost surely, 2^81985889 is an apocalyptic number.

It is an amenable number.

81985889 is a deficient number, since it is larger than the sum of its proper divisors (1).

81985889 is an equidigital number, since it uses as much as digits as its factorization.

81985889 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1658880, while the sum is 56.

The square root of 81985889 is about 9054.6059549822. The cubic root of 81985889 is about 434.4232264244.

The spelling of 81985889 in words is "eighty-one million, nine hundred eighty-five thousand, eight hundred eighty-nine".