66818581 has 4 divisors (see below), whose sum is σ = 69122700. Its totient is φ = 64514464.

The previous prime is 66818567. The next prime is 66818617. The reversal of 66818581 is 18581866.

It is a happy number.

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 23126481 + 43692100 = 4809^2 + 6610^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66818581 is a prime.

It is a super-2 number, since 2×66818581² = 8929445533707122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66818501) 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, 1152016 + ... + 1152073.

It is an arithmetic number, because the mean of its divisors is an integer number (17280675).

Almost surely, 2^66818581 is an apocalyptic number.

It is an amenable number.

66818581 is a deficient number, since it is larger than the sum of its proper divisors (2304119).

66818581 is a wasteful number, since it uses less digits than its factorization.

66818581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2304118.

The product of its digits is 92160, while the sum is 43.

The square root of 66818581 is about 8174.2633307228. The cubic root of 66818581 is about 405.7878906130.

The spelling of 66818581 in words is "sixty-six million, eight hundred eighteen thousand, five hundred eighty-one".