665749372581 has 24 divisors (see below), whose sum is σ = 981364527000. Its totient is φ = 434819860992.

The previous prime is 665749372543. The next prime is 665749372591. The reversal of 665749372581 is 185273947566.

665749372581 is a `hidden beast` number, since 6 + 6 + 5 + 7 + 49 + 3 + 7 + 2 + 581 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 77523264900 + 588226107681 = 278430^2 + 766959^2 .

It is not a de Polignac number, because 665749372581 - 2⁶ = 665749372517 is a prime.

It is a super-2 number, since 2×665749372581² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665749372531) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3725296 + ... + 3899913.

It is an arithmetic number, because the mean of its divisors is an integer number (40890188625).

Almost surely, 2^665749372581 is an apocalyptic number.

It is an amenable number.

665749372581 is a deficient number, since it is larger than the sum of its proper divisors (315615154419).

665749372581 is a wasteful number, since it uses less digits than its factorization.

665749372581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7625413 (or 7625410 counting only the distinct ones).

The product of its digits is 76204800, while the sum is 63.

The spelling of 665749372581 in words is "six hundred sixty-five billion, seven hundred forty-nine million, three hundred seventy-two thousand, five hundred eighty-one".