81378181 has 2 divisors, whose sum is σ = 81378182. Its totient is φ = 81378180.

The previous prime is 81378179. The next prime is 81378191. The reversal of 81378181 is 18187318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78605956 + 2772225 = 8866^2 + 1665^2 .

It is a cyclic number.

It is not a de Polignac number, because 81378181 - 2¹ = 81378179 is a prime.

It is a super-2 number, since 2×81378181² = 13244816685737522, which contains 22 as substring.

Together with 81378179, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81378181.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81378151) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40689090 + 40689091.

It is an arithmetic number, because the mean of its divisors is an integer number (40689091).

Almost surely, 2^81378181 is an apocalyptic number.

It is an amenable number.

81378181 is a deficient number, since it is larger than the sum of its proper divisors (1).

81378181 is an equidigital number, since it uses as much as digits as its factorization.

81378181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10752, while the sum is 37.

The square root of 81378181 is about 9020.9855891693. The cubic root of 81378181 is about 433.3471979127.

The spelling of 81378181 in words is "eighty-one million, three hundred seventy-eight thousand, one hundred eighty-one".