81378191 has 2 divisors, whose sum is σ = 81378192. Its totient is φ = 81378190.

The previous prime is 81378181. The next prime is 81378203. The reversal of 81378191 is 19187318.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81378191 - 2¹⁰ = 81377167 is a prime.

It is a Sophie Germain prime.

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 pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40689095 + 40689096.

It is an arithmetic number, because the mean of its divisors is an integer number (40689096).

Almost surely, 2^81378191 is an apocalyptic number.

81378191 is a deficient number, since it is larger than the sum of its proper divisors (1).

81378191 is an equidigital number, since it uses as much as digits as its factorization.

81378191 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12096, while the sum is 38.

The square root of 81378191 is about 9020.9861434324. The cubic root of 81378191 is about 433.3472156631.

The spelling of 81378191 in words is "eighty-one million, three hundred seventy-eight thousand, one hundred ninety-one".