81909511387 has 16 divisors (see below), whose sum is σ = 91071371520. Its totient is φ = 73034488800.

The previous prime is 81909511379. The next prime is 81909511391. The reversal of 81909511387 is 78311590918.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 81909511387 - 2³ = 81909511379 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81909511337) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1913812 + ... + 1956142.

It is an arithmetic number, because the mean of its divisors is an integer number (5691960720).

Almost surely, 2^81909511387 is an apocalyptic number.

81909511387 is a deficient number, since it is larger than the sum of its proper divisors (9161860133).

81909511387 is a wasteful number, since it uses less digits than its factorization.

81909511387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45714.

The product of its (nonzero) digits is 544320, while the sum is 52.

The spelling of 81909511387 in words is "eighty-one billion, nine hundred nine million, five hundred eleven thousand, three hundred eighty-seven".