666625890661 has 4 divisors (see below), whose sum is σ = 666725260300. Its totient is φ = 666526521024.

The previous prime is 666625890649. The next prime is 666625890703. The reversal of 666625890661 is 166098526666.

It is a happy number.

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 455766761025 + 210859129636 = 675105^2 + 459194^2 .

It is a cyclic number.

It is not a de Polignac number, because 666625890661 - 2¹⁷ = 666625759589 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 666625890661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666625890061) 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, 49674756 + ... + 49688173.

It is an arithmetic number, because the mean of its divisors is an integer number (166681315075).

Almost surely, 2^666625890661 is an apocalyptic number.

It is an amenable number.

666625890661 is a deficient number, since it is larger than the sum of its proper divisors (99369639).

666625890661 is an equidigital number, since it uses as much as digits as its factorization.

666625890661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99369638.

The product of its (nonzero) digits is 33592320, while the sum is 61.

The spelling of 666625890661 in words is "six hundred sixty-six billion, six hundred twenty-five million, eight hundred ninety thousand, six hundred sixty-one".