66788581 has 4 divisors (see below), whose sum is σ = 66867372. Its totient is φ = 66709792.

The previous prime is 66788567. The next prime is 66788609. The reversal of 66788581 is 18588766.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 47128225 + 19660356 = 6865^2 + 4434^2 .

It is a cyclic number.

It is not a de Polignac number, because 66788581 - 2⁹ = 66788069 is a prime.

It is a super-2 number, since 2×66788581² = 8921429103987122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66788681) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 38110 + ... + 39823.

It is an arithmetic number, because the mean of its divisors is an integer number (16716843).

Almost surely, 2^66788581 is an apocalyptic number.

It is an amenable number.

66788581 is a deficient number, since it is larger than the sum of its proper divisors (78791).

66788581 is an equidigital number, since it uses as much as digits as its factorization.

66788581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78790.

The product of its digits is 645120, while the sum is 49.

The square root of 66788581 is about 8172.4280969611. The cubic root of 66788581 is about 405.7271517243.

The spelling of 66788581 in words is "sixty-six million, seven hundred eighty-eight thousand, five hundred eighty-one".