661428505824165 has 24 divisors (see below), whose sum is σ = 1146508932625368. Its totient is φ = 352751760276480.

The previous prime is 661428505824139. The next prime is 661428505824311. The reversal of 661428505824165 is 561428505824166.

661428505824165 is a `hidden beast` number, since 6 + 6 + 1 + 4 + 2 + 8 + 5 + 0 + 582 + 41 + 6 + 5 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 5458162185441 + 655970343638724 = 2336271^2 + 25611918^2 .

It is not a de Polignac number, because 661428505824165 - 2¹⁵ = 661428505791397 is a prime.

It is a super-4 number, since 4×661428505824165⁴ (a number of 60 digits) contains 4444 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 209026696 + ... + 212167425.

It is an arithmetic number, because the mean of its divisors is an integer number (47771205526057).

Almost surely, 2^{661428505824165} is an apocalyptic number.

It is an amenable number.

661428505824165 is a deficient number, since it is larger than the sum of its proper divisors (485080426801203).

661428505824165 is a wasteful number, since it uses less digits than its factorization.

661428505824165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 421229029 (or 421229026 counting only the distinct ones).

The product of its (nonzero) digits is 110592000, while the sum is 63.

Subtracting from 661428505824165 its reverse (561428505824166), we obtain a palindrome (99999999999999).

The spelling of 661428505824165 in words is "six hundred sixty-one trillion, four hundred twenty-eight billion, five hundred five million, eight hundred twenty-four thousand, one hundred sixty-five".