681581 has 4 divisors (see below), whose sum is σ = 721692. Its totient is φ = 641472.

The previous prime is 681563. The next prime is 681589. The reversal of 681581 is 185186.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 185186 = 2 ⋅92593.

It can be written as a sum of positive squares in 2 ways, for example, as 259081 + 422500 = 509^2 + 650^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-681581 is a prime.

It is a super-2 number, since 2×681581² = 929105319122, 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 (681589) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 20030 + ... + 20063.

It is an arithmetic number, because the mean of its divisors is an integer number (180423).

2⁶⁸¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

681581 is a deficient number, since it is larger than the sum of its proper divisors (40111).

681581 is a wasteful number, since it uses less digits than its factorization.

681581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40110.

The product of its digits is 1920, while the sum is 29.

The square root of 681581 is about 825.5791906292. The cubic root of 681581 is about 88.0046915543.

The spelling of 681581 in words is "six hundred eighty-one thousand, five hundred eighty-one".