66865681 has 2 divisors, whose sum is σ = 66865682. Its totient is φ = 66865680.

The previous prime is 66865651. The next prime is 66865717. The reversal of 66865681 is 18656866.

66865681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 60590656 + 6275025 = 7784^2 + 2505^2 .

It is a cyclic number.

It is not a de Polignac number, because 66865681 - 2⁵ = 66865649 is a prime.

It is a super-2 number, since 2×66865681² = 8942038591187522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (66865621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33432840 + 33432841.

It is an arithmetic number, because the mean of its divisors is an integer number (33432841).

Almost surely, 2^66865681 is an apocalyptic number.

It is an amenable number.

66865681 is a deficient number, since it is larger than the sum of its proper divisors (1).

66865681 is an equidigital number, since it uses as much as digits as its factorization.

66865681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 414720, while the sum is 46.

The square root of 66865681 is about 8177.1438167614. The cubic root of 66865681 is about 405.8832140012.

The spelling of 66865681 in words is "sixty-six million, eight hundred sixty-five thousand, six hundred eighty-one".