6665644767681 has 27 divisors (see below), whose sum is σ = 9762680932329. Its totient is φ = 4382517932352.

The previous prime is 6665644767673. The next prime is 6665644767707. The reversal of 6665644767681 is 1867674465666.

The square root of 6665644767681 is 2581791.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 1809280559025 + 4856364208656 = 1345095^2 + 2203716^2 .

It is not a de Polignac number, because 6665644767681 - 2³ = 6665644767673 is a prime.

It is a super-2 number, since 2×6665644767681² (a number of 26 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (6665644717681) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 565406335 + ... + 565418123.

Almost surely, 2^{6665644767681} is an apocalyptic number.

6665644767681 is the 2581791-st square number.

6665644767681 is the 1290896-th centered octagonal number.

It is an amenable number.

6665644767681 is a deficient number, since it is larger than the sum of its proper divisors (3097036164648).

6665644767681 is an frugal number, since it uses more digits than its factorization.

6665644767681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23730 (or 11865 counting only the distinct ones).

The product of its digits is 1463132160, while the sum is 72.

The spelling of 6665644767681 in words is "six trillion, six hundred sixty-five billion, six hundred forty-four million, seven hundred sixty-seven thousand, six hundred eighty-one".