666561661653 has 32 divisors (see below), whose sum is σ = 983529907200. Its totient is φ = 399403927296.

The previous prime is 666561661637. The next prime is 666561661657. The reversal of 666561661653 is 356166165666.

It is a happy number.

It is not a de Polignac number, because 666561661653 - 2⁴ = 666561661637 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 666561661593 and 666561661602.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666561661657) 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, 267078 + ... + 1185096.

It is an arithmetic number, because the mean of its divisors is an integer number (30735309600).

Almost surely, 2^666561661653 is an apocalyptic number.

It is an amenable number.

666561661653 is a deficient number, since it is larger than the sum of its proper divisors (316968245547).

666561661653 is a wasteful number, since it uses less digits than its factorization.

666561661653 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 918681.

The product of its digits is 20995200, while the sum is 57.

The spelling of 666561661653 in words is "six hundred sixty-six billion, five hundred sixty-one million, six hundred sixty-one thousand, six hundred fifty-three".