81566266517 has 4 divisors (see below), whose sum is σ = 83463156480. Its totient is φ = 79669376556.

The previous prime is 81566266511. The next prime is 81566266519. The reversal of 81566266517 is 71566266518.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81566266517 - 2⁴ = 81566266501 is a prime.

It is a super-2 number, since 2×81566266517² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81566266511) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 948444917 + ... + 948445002.

It is an arithmetic number, because the mean of its divisors is an integer number (20865789120).

Almost surely, 2^81566266517 is an apocalyptic number.

It is an amenable number.

81566266517 is a deficient number, since it is larger than the sum of its proper divisors (1896889963).

81566266517 is a wasteful number, since it uses less digits than its factorization.

81566266517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1896889962.

The product of its digits is 3628800, while the sum is 53.

Subtracting from 81566266517 its reverse (71566266518), we obtain a palindrome (9999999999).

The spelling of 81566266517 in words is "eighty-one billion, five hundred sixty-six million, two hundred sixty-six thousand, five hundred seventeen".