81381544081 has 2 divisors, whose sum is σ = 81381544082. Its totient is φ = 81381544080.

The previous prime is 81381544063. The next prime is 81381544103. The reversal of 81381544081 is 18044518318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 44521000000 + 36860544081 = 211000^2 + 191991^2 .

It is a cyclic number.

It is not a de Polignac number, because 81381544081 - 2⁷ = 81381543953 is a prime.

It is a super-2 number, since 2×81381544081² (a number of 23 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81381544001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40690772040 + 40690772041.

It is an arithmetic number, because the mean of its divisors is an integer number (40690772041).

Almost surely, 2^81381544081 is an apocalyptic number.

It is an amenable number.

81381544081 is a deficient number, since it is larger than the sum of its proper divisors (1).

81381544081 is an equidigital number, since it uses as much as digits as its factorization.

81381544081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 122880, while the sum is 43.

The spelling of 81381544081 in words is "eighty-one billion, three hundred eighty-one million, five hundred forty-four thousand, eighty-one".