66781538717 has 4 divisors (see below), whose sum is σ = 66782067036. Its totient is φ = 66781010400.

The previous prime is 66781538711. The next prime is 66781538731. The reversal of 66781538717 is 71783518766.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 6731546116 + 60049992601 = 82046^2 + 245051^2 .

It is a cyclic number.

It is not a de Polignac number, because 66781538717 - 2¹⁶ = 66781473181 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 (66781538711) 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, 49943 + ... + 368859.

It is an arithmetic number, because the mean of its divisors is an integer number (16695516759).

Almost surely, 2^66781538717 is an apocalyptic number.

It is an amenable number.

66781538717 is a deficient number, since it is larger than the sum of its proper divisors (528319).

66781538717 is a wasteful number, since it uses less digits than its factorization.

66781538717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 528318.

The product of its digits is 11854080, while the sum is 59.

The spelling of 66781538717 in words is "sixty-six billion, seven hundred eighty-one million, five hundred thirty-eight thousand, seven hundred seventeen".