81401891 has 2 divisors, whose sum is σ = 81401892. Its totient is φ = 81401890.

The previous prime is 81401839. The next prime is 81401893. The reversal of 81401891 is 19810418.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81401891 - 2²² = 77207587 is a prime.

It is a Sophie Germain prime.

Together with 81401893, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81401893) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40700945 + 40700946.

It is an arithmetic number, because the mean of its divisors is an integer number (40700946).

Almost surely, 2^81401891 is an apocalyptic number.

81401891 is a deficient number, since it is larger than the sum of its proper divisors (1).

81401891 is an equidigital number, since it uses as much as digits as its factorization.

81401891 is an odious number, because the sum of its binary digits is odd.

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

The square root of 81401891 is about 9022.2996514193. The cubic root of 81401891 is about 433.3892798903.

The spelling of 81401891 in words is "eighty-one million, four hundred one thousand, eight hundred ninety-one".