81125308561 has 4 divisors (see below), whose sum is σ = 88500336624. Its totient is φ = 73750280500.

The previous prime is 81125308519. The next prime is 81125308571. The reversal of 81125308561 is 16580352118.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81125308561 - 2⁹ = 81125308049 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81125308571) 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 in 3 ways as a sum of consecutive naturals, for example, 3687514015 + ... + 3687514036.

It is an arithmetic number, because the mean of its divisors is an integer number (22125084156).

Almost surely, 2^81125308561 is an apocalyptic number.

It is an amenable number.

81125308561 is a deficient number, since it is larger than the sum of its proper divisors (7375028063).

81125308561 is a wasteful number, since it uses less digits than its factorization.

81125308561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7375028062.

The product of its (nonzero) digits is 57600, while the sum is 40.

The spelling of 81125308561 in words is "eighty-one billion, one hundred twenty-five million, three hundred eight thousand, five hundred sixty-one".