81786719578 has 4 divisors (see below), whose sum is σ = 122680079370. Its totient is φ = 40893359788.

The previous prime is 81786719537. The next prime is 81786719579. The reversal of 81786719578 is 87591768718.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 79962831729 + 1823887849 = 282777^2 + 42707^2 .

It is a Smith number, since the sum of its digits (67) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (81786719579) 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, 20446679893 + ... + 20446679896.

Almost surely, 2^81786719578 is an apocalyptic number.

81786719578 is a deficient number, since it is larger than the sum of its proper divisors (40893359792).

81786719578 is a wasteful number, since it uses less digits than its factorization.

81786719578 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40893359791.

The product of its digits is 47416320, while the sum is 67.

The spelling of 81786719578 in words is "eighty-one billion, seven hundred eighty-six million, seven hundred nineteen thousand, five hundred seventy-eight".