2581 has 4 divisors (see below), whose sum is σ = 2700. Its totient is φ = 2464.

The previous prime is 2579. The next prime is 2591. The reversal of 2581 is 1852.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 900 + 1681 = 30^2 + 41^2 .

It is a cyclic number.

It is not a de Polignac number, because 2581 - 2¹ = 2579 is a prime.

It is a super-2 number, since 2×2581² = 13323122, which contains 22 as substring.

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a plaindrome in base 9 and base 13.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2521) 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, 16 + ... + 73.

It is an arithmetic number, because the mean of its divisors is an integer number (675).

2²⁵⁸¹ is an apocalyptic number.

It is an amenable number.

2581 is a deficient number, since it is larger than the sum of its proper divisors (119).

2581 is an equidigital number, since it uses as much as digits as its factorization.

2581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 118.

The product of its digits is 80, while the sum is 16.

The square root of 2581 is about 50.8035431835. The cubic root of 2581 is about 13.7171114796.

Subtracting from 2581 its reverse (1852), we obtain a 6-th power (729 = 3⁶).

It can be divided in two parts, 25 and 81, that multiplied together give a square (2025 = 45²).

The spelling of 2581 in words is "two thousand, five hundred eighty-one".