81994508809 has 2 divisors, whose sum is σ = 81994508810. Its totient is φ = 81994508808.

The previous prime is 81994508767. The next prime is 81994508839. The reversal of 81994508809 is 90880549918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66991933584 + 15002575225 = 258828^2 + 122485^2 .

It is a cyclic number.

It is not a de Polignac number, because 81994508809 - 2²⁵ = 81960954377 is a prime.

It is not a weakly prime, because it can be changed into another prime (81994508839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40997254404 + 40997254405.

It is an arithmetic number, because the mean of its divisors is an integer number (40997254405).

Almost surely, 2^81994508809 is an apocalyptic number.

It is an amenable number.

81994508809 is a deficient number, since it is larger than the sum of its proper divisors (1).

81994508809 is an equidigital number, since it uses as much as digits as its factorization.

81994508809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7464960, while the sum is 61.

The spelling of 81994508809 in words is "eighty-one billion, nine hundred ninety-four million, five hundred eight thousand, eight hundred nine".