81561073187 has 16 divisors (see below), whose sum is σ = 89380101888. Its totient is φ = 73809864480.

The previous prime is 81561073177. The next prime is 81561073199. The reversal of 81561073187 is 78137016518.

It is not a de Polignac number, because 81561073187 - 2⁶ = 81561073123 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81561073127) 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, 4193828 + ... + 4213230.

It is an arithmetic number, because the mean of its divisors is an integer number (5586256368).

Almost surely, 2^81561073187 is an apocalyptic number.

81561073187 is a deficient number, since it is larger than the sum of its proper divisors (7819028701).

81561073187 is a wasteful number, since it uses less digits than its factorization.

81561073187 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21130.

The product of its (nonzero) digits is 282240, while the sum is 47.

The spelling of 81561073187 in words is "eighty-one billion, five hundred sixty-one million, seventy-three thousand, one hundred eighty-seven".