66581 has 4 divisors (see below), whose sum is σ = 67200. Its totient is φ = 65964.

The previous prime is 66571. The next prime is 66587. The reversal of 66581 is 18566.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 18566 = 2 ⋅9283.

It is a cyclic number.

It is not a de Polignac number, because 66581 - 2¹⁰ = 65557 is a prime.

It is a super-2 number, since 2×66581² = 8866059122, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 9.

It is a self number, because there is not a number n which added to its sum of digits gives 66581.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66587) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 101 + ... + 378.

It is an arithmetic number, because the mean of its divisors is an integer number (16800).

2⁶⁶⁵⁸¹ is an apocalyptic number.

It is an amenable number.

66581 is a deficient number, since it is larger than the sum of its proper divisors (619).

66581 is a wasteful number, since it uses less digits than its factorization.

66581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 618.

The product of its digits is 1440, while the sum is 26.

The square root of 66581 is about 258.0329436332. The cubic root of 66581 is about 40.5306377935.

The spelling of 66581 in words is "sixty-six thousand, five hundred eighty-one".