81209640779 has 2 divisors, whose sum is σ = 81209640780. Its totient is φ = 81209640778.

The previous prime is 81209640773. The next prime is 81209640793. The reversal of 81209640779 is 97704690218.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81209640779 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81209640779.

It is not a weakly prime, because it can be changed into another prime (81209640773) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40604820389 + 40604820390.

It is an arithmetic number, because the mean of its divisors is an integer number (40604820390).

Almost surely, 2^81209640779 is an apocalyptic number.

81209640779 is a deficient number, since it is larger than the sum of its proper divisors (1).

81209640779 is an equidigital number, since it uses as much as digits as its factorization.

81209640779 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1524096, while the sum is 53.

The spelling of 81209640779 in words is "eighty-one billion, two hundred nine million, six hundred forty thousand, seven hundred seventy-nine".