81756192391 has 4 divisors (see below), whose sum is σ = 81757679400. Its totient is φ = 81754705384.

The previous prime is 81756192373. The next prime is 81756192407. The reversal of 81756192391 is 19329165718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19329165718 = 2 ⋅9664582859.

It is a cyclic number.

It is not a de Polignac number, because 81756192391 - 2¹⁹ = 81755668103 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81756192341) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 657736 + ... + 772093.

It is an arithmetic number, because the mean of its divisors is an integer number (20439419850).

Almost surely, 2^81756192391 is an apocalyptic number.

81756192391 is a deficient number, since it is larger than the sum of its proper divisors (1487009).

81756192391 is a wasteful number, since it uses less digits than its factorization.

81756192391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1487008.

The product of its digits is 816480, while the sum is 52.

The spelling of 81756192391 in words is "eighty-one billion, seven hundred fifty-six million, one hundred ninety-two thousand, three hundred ninety-one".