81931208905 has 32 divisors (see below), whose sum is σ = 121027302144. Its totient is φ = 51850665216.

The previous prime is 81931208899. The next prime is 81931208911. The reversal of 81931208905 is 50980213918.

It is an interprime number because it is at equal distance from previous prime (81931208899) and next prime (81931208911).

It is not a de Polignac number, because 81931208905 - 2³ = 81931208897 is a prime.

It is an unprimeable number.

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 31 ways as a sum of consecutive naturals, for example, 3389994 + ... + 3414076.

It is an arithmetic number, because the mean of its divisors is an integer number (3782103192).

Almost surely, 2^81931208905 is an apocalyptic number.

It is an amenable number.

81931208905 is a deficient number, since it is larger than the sum of its proper divisors (39096093239).

81931208905 is a wasteful number, since it uses less digits than its factorization.

81931208905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31585.

The product of its (nonzero) digits is 155520, while the sum is 46.

The spelling of 81931208905 in words is "eighty-one billion, nine hundred thirty-one million, two hundred eight thousand, nine hundred five".