81000891891 has 10 divisors (see below), whose sum is σ = 121001332452. Its totient is φ = 54000594540.

The previous prime is 81000891883. The next prime is 81000891893. The reversal of 81000891891 is 19819800018.

It is not a de Polignac number, because 81000891891 - 2³ = 81000891883 is a prime.

It is a super-2 number, since 2×81000891891² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81000891893) 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 in 9 ways as a sum of consecutive naturals, for example, 500005425 + ... + 500005586.

Almost surely, 2^81000891891 is an apocalyptic number.

81000891891 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

81000891891 is a deficient number, since it is larger than the sum of its proper divisors (40000440561).

81000891891 is a wasteful number, since it uses less digits than its factorization.

81000891891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1000011023 (or 1000011014 counting only the distinct ones).

The product of its (nonzero) digits is 41472, while the sum is 45.

The spelling of 81000891891 in words is "eighty-one billion, eight hundred ninety-one thousand, eight hundred ninety-one".