65581 has 2 divisors, whose sum is σ = 65582. Its totient is φ = 65580.

The previous prime is 65579. The next prime is 65587. The reversal of 65581 is 18556.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 38025 + 27556 = 195^2 + 166^2 .

It is a cyclic number.

It is not a de Polignac number, because 65581 - 2¹ = 65579 is a prime.

It is a super-2 number, since 2×65581² = 8601735122, which contains 22 as substring.

Together with 65579, it forms a pair of twin primes.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (65587) 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 as a sum of consecutive naturals, namely, 32790 + 32791.

It is an arithmetic number, because the mean of its divisors is an integer number (32791).

2⁶⁵⁵⁸¹ is an apocalyptic number.

It is an amenable number.

65581 is a deficient number, since it is larger than the sum of its proper divisors (1).

65581 is an equidigital number, since it uses as much as digits as its factorization.

65581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1200, while the sum is 25.

The square root of 65581 is about 256.0878755428. The cubic root of 65581 is about 40.3266994227.

Subtracting from 65581 its sum of digits (25), we obtain a palindrome (65556).

It can be divided in two parts, 65 and 581, that added together give a palindrome (646).

The spelling of 65581 in words is "sixty-five thousand, five hundred eighty-one".