201581 has 2 divisors, whose sum is σ = 201582. Its totient is φ = 201580.

The previous prime is 201577. The next prime is 201589. The reversal of 201581 is 185102.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 188356 + 13225 = 434^2 + 115^2 .

It is a cyclic number.

It is not a de Polignac number, because 201581 - 2² = 201577 is a prime.

It is a super-2 number, since 2×201581² = 81269799122, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (201589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 100790 + 100791.

It is an arithmetic number, because the mean of its divisors is an integer number (100791).

2²⁰¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

201581 is a deficient number, since it is larger than the sum of its proper divisors (1).

201581 is an equidigital number, since it uses as much as digits as its factorization.

201581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 80, while the sum is 17.

The square root of 201581 is about 448.9777277327. The cubic root of 201581 is about 58.6340462307.

Adding to 201581 its reverse (185102), we get a palindrome (386683).

The spelling of 201581 in words is "two hundred one thousand, five hundred eighty-one".