81240385891 has 32 divisors (see below), whose sum is σ = 96691212800. Its totient is φ = 68212821600.

The previous prime is 81240385823. The next prime is 81240385909. The reversal of 81240385891 is 19858304218.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-81240385891 is a prime.

It is a hoax number, since the sum of its digits (49) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (49).

It is not an unprimeable number, because it can be changed into a prime (81240385091) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4149796 + ... + 4169326.

It is an arithmetic number, because the mean of its divisors is an integer number (3021600400).

Almost surely, 2^81240385891 is an apocalyptic number.

81240385891 is a deficient number, since it is larger than the sum of its proper divisors (15450826909).

81240385891 is a wasteful number, since it uses less digits than its factorization.

81240385891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19800 (or 19786 counting only the distinct ones).

The product of its (nonzero) digits is 552960, while the sum is 49.

The spelling of 81240385891 in words is "eighty-one billion, two hundred forty million, three hundred eighty-five thousand, eight hundred ninety-one".