66351681 has 48 divisors (see below), whose sum is σ = 109624320. Its totient is φ = 38623200.

The previous prime is 66351569. The next prime is 66351683. The reversal of 66351681 is 18615366.

It is a happy number.

66351681 is a `hidden beast` number, since 6 + 63 + 516 + 81 = 666.

66351681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 66351681 - 2²² = 62157377 is a prime.

It is a super-2 number, since 2×66351681² = 8805091143051522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (66351683) 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 in 47 ways as a sum of consecutive naturals, for example, 347296 + ... + 347486.

It is an arithmetic number, because the mean of its divisors is an integer number (2283840).

Almost surely, 2^66351681 is an apocalyptic number.

It is an amenable number.

66351681 is a deficient number, since it is larger than the sum of its proper divisors (43272639).

66351681 is a wasteful number, since it uses less digits than its factorization.

66351681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 259 (or 234 counting only the distinct ones).

The product of its digits is 25920, while the sum is 36.

The square root of 66351681 is about 8145.6541173806. The cubic root of 66351681 is about 404.8405224872.

The spelling of 66351681 in words is "sixty-six million, three hundred fifty-one thousand, six hundred eighty-one".