81911881 has 2 divisors, whose sum is σ = 81911882. Its totient is φ = 81911880.

The previous prime is 81911873. The next prime is 81911887. The reversal of 81911881 is 18811918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81812025 + 99856 = 9045^2 + 316^2 .

It is a cyclic number.

It is not a de Polignac number, because 81911881 - 2³ = 81911873 is a prime.

It is a super-2 number, since 2×81911881² = 13419112497916322, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81911881.

It is not a weakly prime, because it can be changed into another prime (81911887) 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, 40955940 + 40955941.

It is an arithmetic number, because the mean of its divisors is an integer number (40955941).

Almost surely, 2^81911881 is an apocalyptic number.

It is an amenable number.

81911881 is a deficient number, since it is larger than the sum of its proper divisors (1).

81911881 is an equidigital number, since it uses as much as digits as its factorization.

81911881 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 37.

The square root of 81911881 is about 9050.5182724527. The cubic root of 81911881 is about 434.2924702927.

Adding to 81911881 its sum of digits (37), we get a palindrome (81911918).

The spelling of 81911881 in words is "eighty-one million, nine hundred eleven thousand, eight hundred eighty-one".