81810535378181 has 4 divisors (see below), whose sum is σ = 82225817283852. Its totient is φ = 81395253472512.

The previous prime is 81810535378163. The next prime is 81810535378207. The reversal of 81810535378181 is 18187353501818.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 66477116222500 + 15333419155681 = 8153350^2 + 3915791^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81810535378181 is a prime.

It is a super-2 number, since 2×81810535378181² (a number of 29 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81810535378181.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81810535378111) 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, 207640952540 + ... + 207640952933.

It is an arithmetic number, because the mean of its divisors is an integer number (20556454320963).

Almost surely, 2^{81810535378181} is an apocalyptic number.

It is an amenable number.

81810535378181 is a deficient number, since it is larger than the sum of its proper divisors (415281905671).

81810535378181 is a wasteful number, since it uses less digits than its factorization.

81810535378181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 415281905670.

The product of its (nonzero) digits is 6451200, while the sum is 59.

Adding to 81810535378181 its reverse (18187353501818), we get a palindrome (99997888879999).

The spelling of 81810535378181 in words is "eighty-one trillion, eight hundred ten billion, five hundred thirty-five million, three hundred seventy-eight thousand, one hundred eighty-one".