81642057785 has 4 divisors (see below), whose sum is σ = 97970469348. Its totient is φ = 65313646224.

The previous prime is 81642057781. The next prime is 81642057797. The reversal of 81642057785 is 58775024618.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 41868935161 + 39773122624 = 204619^2 + 199432^2 .

It is a cyclic number.

It is not a de Polignac number, because 81642057785 - 2² = 81642057781 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81642057781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8164205774 + ... + 8164205783.

It is an arithmetic number, because the mean of its divisors is an integer number (24492617337).

Almost surely, 2^81642057785 is an apocalyptic number.

It is an amenable number.

81642057785 is a deficient number, since it is larger than the sum of its proper divisors (16328411563).

81642057785 is a wasteful number, since it uses less digits than its factorization.

81642057785 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16328411562.

The product of its (nonzero) digits is 3763200, while the sum is 53.

The spelling of 81642057785 in words is "eighty-one billion, six hundred forty-two million, fifty-seven thousand, seven hundred eighty-five".