81816508861 has 8 divisors (see below), whose sum is σ = 82108582200. Its totient is φ = 81524631552.

The previous prime is 81816508847. The next prime is 81816508877. The reversal of 81816508861 is 16880561818.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 935992836 + 80880516025 = 30594^2 + 284395^2 .

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 81816508861 - 2¹⁹ = 81815984573 is a prime.

It is a super-2 number, since 2×81816508861² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81816508799 and 81816508808.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81816508061) 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, 814215 + ... + 909163.

It is an arithmetic number, because the mean of its divisors is an integer number (10263572775).

Almost surely, 2^81816508861 is an apocalyptic number.

It is an amenable number.

81816508861 is a deficient number, since it is larger than the sum of its proper divisors (292073339).

81816508861 is a wasteful number, since it uses less digits than its factorization.

81816508861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 98015.

The product of its (nonzero) digits is 737280, while the sum is 52.

The spelling of 81816508861 in words is "eighty-one billion, eight hundred sixteen million, five hundred eight thousand, eight hundred sixty-one".