81140266561 has 4 divisors (see below), whose sum is σ = 81142408900. Its totient is φ = 81138124224.

The previous prime is 81140266547. The next prime is 81140266579. The reversal of 81140266561 is 16566204118.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16566204118 = 2 ⋅8283102059.

It can be written as a sum of positive squares in 2 ways, for example, as 43758364225 + 37381902336 = 209185^2 + 193344^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81140266561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81140266861) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1013316 + ... + 1090453.

It is an arithmetic number, because the mean of its divisors is an integer number (20285602225).

Almost surely, 2^81140266561 is an apocalyptic number.

It is an amenable number.

81140266561 is a deficient number, since it is larger than the sum of its proper divisors (2142339).

81140266561 is a wasteful number, since it uses less digits than its factorization.

81140266561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2142338.

The product of its (nonzero) digits is 69120, while the sum is 40.

The spelling of 81140266561 in words is "eighty-one billion, one hundred forty million, two hundred sixty-six thousand, five hundred sixty-one".