205611661 has 2 divisors, whose sum is σ = 205611662. Its totient is φ = 205611660.

The previous prime is 205611643. The next prime is 205611683. The reversal of 205611661 is 166116502.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 127554436 + 78057225 = 11294^2 + 8835^2 .

It is a cyclic number.

It is not a de Polignac number, because 205611661 - 2⁷ = 205611533 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205611061) 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 as a sum of consecutive naturals, namely, 102805830 + 102805831.

It is an arithmetic number, because the mean of its divisors is an integer number (102805831).

Almost surely, 2^205611661 is an apocalyptic number.

It is an amenable number.

205611661 is a deficient number, since it is larger than the sum of its proper divisors (1).

205611661 is an equidigital number, since it uses as much as digits as its factorization.

205611661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 205611661 is about 14339.1652825400. The cubic root of 205611661 is about 590.2227072676. Note that the first 3 decimals are identical.

It can be divided in two parts, 20561 and 1661, that added together give a palindrome (22222).

The spelling of 205611661 in words is "two hundred five million, six hundred eleven thousand, six hundred sixty-one".