205661 has 2 divisors, whose sum is σ = 205662. Its totient is φ = 205660.

The previous prime is 205657. The next prime is 205663. The reversal of 205661 is 166502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 109561 + 96100 = 331^2 + 310^2 .

It is a cyclic number.

It is not a de Polignac number, because 205661 - 2² = 205657 is a prime.

Together with 205663, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102830 + 102831.

It is an arithmetic number, because the mean of its divisors is an integer number (102831).

2²⁰⁵⁶⁶¹ is an apocalyptic number.

It is an amenable number.

205661 is a deficient number, since it is larger than the sum of its proper divisors (1).

205661 is an equidigital number, since it uses as much as digits as its factorization.

205661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 205661 is about 453.4986218281. The cubic root of 205661 is about 59.0269913846.

The spelling of 205661 in words is "two hundred five thousand, six hundred sixty-one".