209581 has 2 divisors, whose sum is σ = 209582. Its totient is φ = 209580.

The previous prime is 209579. The next prime is 209597. The reversal of 209581 is 185902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 133956 + 75625 = 366^2 + 275^2 .

It is a cyclic number.

It is not a de Polignac number, because 209581 - 2¹ = 209579 is a prime.

It is a super-2 number, since 2×209581² = 87848391122, which contains 22 as substring.

Together with 209579, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (209381) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104790 + 104791.

It is an arithmetic number, because the mean of its divisors is an integer number (104791).

2²⁰⁹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

209581 is a deficient number, since it is larger than the sum of its proper divisors (1).

209581 is an equidigital number, since it uses as much as digits as its factorization.

209581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 720, while the sum is 25.

The square root of 209581 is about 457.8001747488. The cubic root of 209581 is about 59.3996614083.

The spelling of 209581 in words is "two hundred nine thousand, five hundred eighty-one".