81666741561 has 8 divisors (see below), whose sum is σ = 108891445344. Its totient is φ = 54443266080.

The previous prime is 81666741553. The next prime is 81666741577. The reversal of 81666741561 is 16514766618.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81666741561 - 2³ = 81666741553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81666741511) 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 7 ways as a sum of consecutive naturals, for example, 138756 + ... + 427301.

It is an arithmetic number, because the mean of its divisors is an integer number (13611430668).

Almost surely, 2^81666741561 is an apocalyptic number.

It is an amenable number.

81666741561 is a deficient number, since it is larger than the sum of its proper divisors (27224703783).

81666741561 is a wasteful number, since it uses less digits than its factorization.

81666741561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 614151.

The product of its digits is 1451520, while the sum is 51.

The spelling of 81666741561 in words is "eighty-one billion, six hundred sixty-six million, seven hundred forty-one thousand, five hundred sixty-one".