66115861681 has 2 divisors, whose sum is σ = 66115861682. Its totient is φ = 66115861680.

The previous prime is 66115861529. The next prime is 66115861711. The reversal of 66115861681 is 18616851166.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 44531550625 + 21584311056 = 211025^2 + 146916^2 .

It is a cyclic number.

It is not a de Polignac number, because 66115861681 - 2⁹ = 66115861169 is a prime.

It is a super-2 number, since 2×66115861681² (a number of 22 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (66115801681) 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 as a sum of consecutive naturals, namely, 33057930840 + 33057930841.

It is an arithmetic number, because the mean of its divisors is an integer number (33057930841).

Almost surely, 2^66115861681 is an apocalyptic number.

It is an amenable number.

66115861681 is a deficient number, since it is larger than the sum of its proper divisors (1).

66115861681 is an equidigital number, since it uses as much as digits as its factorization.

66115861681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 414720, while the sum is 49.

The spelling of 66115861681 in words is "sixty-six billion, one hundred fifteen million, eight hundred sixty-one thousand, six hundred eighty-one".