81555643681 has 8 divisors (see below), whose sum is σ = 87941901600. Its totient is φ = 75378771360.

The previous prime is 81555643661. The next prime is 81555643691. The reversal of 81555643681 is 18634655518.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 81555643681 - 2⁵ = 81555643649 is a prime.

It is a super-2 number, since 2×81555643681² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81555643621) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 52345591 + ... + 52347148.

It is an arithmetic number, because the mean of its divisors is an integer number (10992737700).

Almost surely, 2^81555643681 is an apocalyptic number.

It is an amenable number.

81555643681 is a deficient number, since it is larger than the sum of its proper divisors (6386257919).

81555643681 is a wasteful number, since it uses less digits than its factorization.

81555643681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 104692799.

The product of its digits is 3456000, while the sum is 52.

The spelling of 81555643681 in words is "eighty-one billion, five hundred fifty-five million, six hundred forty-three thousand, six hundred eighty-one".