666261756016021 has 4 divisors (see below), whose sum is σ = 726831006562944. Its totient is φ = 605692505469100.

The previous prime is 666261756016009. The next prime is 666261756016039. The reversal of 666261756016021 is 120610657162666.

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 666261756016021 - 2²⁵ = 666261722461589 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666261756016121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30284625273445 + ... + 30284625273466.

It is an arithmetic number, because the mean of its divisors is an integer number (181707751640736).

Almost surely, 2^{666261756016021} is an apocalyptic number.

It is an amenable number.

666261756016021 is a deficient number, since it is larger than the sum of its proper divisors (60569250546923).

666261756016021 is a wasteful number, since it uses less digits than its factorization.

666261756016021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60569250546922.

The product of its (nonzero) digits is 6531840, while the sum is 55.

The spelling of 666261756016021 in words is "six hundred sixty-six trillion, two hundred sixty-one billion, seven hundred fifty-six million, sixteen thousand, twenty-one".