491581 has 2 divisors, whose sum is σ = 491582. Its totient is φ = 491580.

The previous prime is 491539. The next prime is 491591. The reversal of 491581 is 185194.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 280900 + 210681 = 530^2 + 459^2 .

It is a cyclic number.

It is not a de Polignac number, because 491581 - 2¹³ = 483389 is a prime.

It is a super-2 number, since 2×491581² = 483303759122, which contains 22 as substring.

It is a Chen prime.

It is equal to p₄₀₈₈₈ and since 491581 and 40888 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (491501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 245790 + 245791.

It is an arithmetic number, because the mean of its divisors is an integer number (245791).

2⁴⁹¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

491581 is a deficient number, since it is larger than the sum of its proper divisors (1).

491581 is an equidigital number, since it uses as much as digits as its factorization.

491581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1440, while the sum is 28.

The square root of 491581 is about 701.1283762622. The cubic root of 491581 is about 78.9220509774.

The spelling of 491581 in words is "four hundred ninety-one thousand, five hundred eighty-one".