191581 has 4 divisors (see below), whose sum is σ = 206332. Its totient is φ = 176832.

The previous prime is 191579. The next prime is 191599. The reversal of 191581 is 185191.

191581 = 309² + 310².

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 185191 = 109 ⋅1699.

It can be written as a sum of positive squares in 2 ways, for example, as 95481 + 96100 = 309^2 + 310^2 .

It is a cyclic number.

It is not a de Polignac number, because 191581 - 2¹ = 191579 is a prime.

It is a super-2 number, since 2×191581² = 73406559122, 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 (191531) 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, 7356 + ... + 7381.

It is an arithmetic number, because the mean of its divisors is an integer number (51583).

2¹⁹¹⁵⁸¹ is an apocalyptic number.

191581 is the 310-th centered square number.

It is an amenable number.

191581 is a deficient number, since it is larger than the sum of its proper divisors (14751).

191581 is a wasteful number, since it uses less digits than its factorization.

191581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14750.

The product of its digits is 360, while the sum is 25.

The square root of 191581 is about 437.6996687227. The cubic root of 191581 is about 57.6479867920.

It can be divided in two parts, 19 and 1581, that added together give a square (1600 = 40²).

The spelling of 191581 in words is "one hundred ninety-one thousand, five hundred eighty-one".