665666650591 has 4 divisors (see below), whose sum is σ = 687139768384. Its totient is φ = 644193532800.

The previous prime is 665666650589. The next prime is 665666650603. The reversal of 665666650591 is 195056666566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 195056666566 = 2 ⋅97528333283.

It is a cyclic number.

It is not a de Polignac number, because 665666650591 - 2¹ = 665666650589 is a prime.

It is a super-2 number, since 2×665666650591² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665666650391) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10736558850 + ... + 10736558911.

It is an arithmetic number, because the mean of its divisors is an integer number (171784942096).

Almost surely, 2^665666650591 is an apocalyptic number.

665666650591 is a deficient number, since it is larger than the sum of its proper divisors (21473117793).

665666650591 is a wasteful number, since it uses less digits than its factorization.

665666650591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21473117792.

The product of its (nonzero) digits is 52488000, while the sum is 61.

The spelling of 665666650591 in words is "six hundred sixty-five billion, six hundred sixty-six million, six hundred fifty thousand, five hundred ninety-one".