81209640773 has 2 divisors, whose sum is σ = 81209640774. Its totient is φ = 81209640772.

The previous prime is 81209640739. The next prime is 81209640779. The reversal of 81209640773 is 37704690218.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76653120769 + 4556520004 = 276863^2 + 67502^2 .

It is a cyclic number.

It is not a de Polignac number, because 81209640773 - 2⁶ = 81209640709 is a prime.

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 (81209640779) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40604820386 + 40604820387.

It is an arithmetic number, because the mean of its divisors is an integer number (40604820387).

Almost surely, 2^81209640773 is an apocalyptic number.

It is an amenable number.

81209640773 is a deficient number, since it is larger than the sum of its proper divisors (1).

81209640773 is an equidigital number, since it uses as much as digits as its factorization.

81209640773 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 508032, while the sum is 47.

The spelling of 81209640773 in words is "eighty-one billion, two hundred nine million, six hundred forty thousand, seven hundred seventy-three".