666988424889665 has 4 divisors (see below), whose sum is σ = 800386109867604. Its totient is φ = 533590739911728.

The previous prime is 666988424889649. The next prime is 666988424889667. The reversal of 666988424889665 is 566988424889666.

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 158287826400001 + 508700598489664 = 12581249^2 + 22554392^2 .

It is a cyclic number.

It is not a de Polignac number, because 666988424889665 - 2⁴ = 666988424889649 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (666988424889667) 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, 66698842488962 + ... + 66698842488971.

It is an arithmetic number, because the mean of its divisors is an integer number (200096527466901).

Almost surely, 2^{666988424889665} is an apocalyptic number.

It is an amenable number.

666988424889665 is a deficient number, since it is larger than the sum of its proper divisors (133397684977939).

666988424889665 is a wasteful number, since it uses less digits than its factorization.

666988424889665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133397684977938.

The product of its digits is 412782428160, while the sum is 95.

Subtracting from 666988424889665 its reverse (566988424889666), we obtain a palindrome (99999999999999).

The spelling of 666988424889665 in words is "six hundred sixty-six trillion, nine hundred eighty-eight billion, four hundred twenty-four million, eight hundred eighty-nine thousand, six hundred sixty-five".