81616181 has 4 divisors (see below), whose sum is σ = 82424364. Its totient is φ = 80808000.

The previous prime is 81616177. The next prime is 81616217. The reversal of 81616181 is 18161618.

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 78605956 + 3010225 = 8866^2 + 1735^2 .

It is a cyclic number.

It is not a de Polignac number, because 81616181 - 2² = 81616177 is a prime.

It is a super-2 number, since 2×81616181² = 13322402002049522, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81616681) 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, 403940 + ... + 404141.

It is an arithmetic number, because the mean of its divisors is an integer number (20606091).

Almost surely, 2^81616181 is an apocalyptic number.

It is an amenable number.

81616181 is a deficient number, since it is larger than the sum of its proper divisors (808183).

81616181 is a wasteful number, since it uses less digits than its factorization.

81616181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 808182.

The product of its digits is 2304, while the sum is 32.

The square root of 81616181 is about 9034.1674215170. The cubic root of 81616181 is about 433.7692449112.

Adding to 81616181 its reverse (18161618), we get a palindrome (99777799).

The spelling of 81616181 in words is "eighty-one million, six hundred sixteen thousand, one hundred eighty-one".