81557291643 has 32 divisors (see below), whose sum is σ = 113431169280. Its totient is φ = 52080900480.

The previous prime is 81557291633. The next prime is 81557291671. The reversal of 81557291643 is 34619275518.

It is not a de Polignac number, because 81557291643 - 2⁹ = 81557291131 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81557291633) 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, 3191505 + ... + 3216957.

It is an arithmetic number, because the mean of its divisors is an integer number (3544724040).

Almost surely, 2^81557291643 is an apocalyptic number.

81557291643 is a deficient number, since it is larger than the sum of its proper divisors (31873877637).

81557291643 is a wasteful number, since it uses less digits than its factorization.

81557291643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25979.

The product of its digits is 1814400, while the sum is 51.

The spelling of 81557291643 in words is "eighty-one billion, five hundred fifty-seven million, two hundred ninety-one thousand, six hundred forty-three".