205865981 has 2 divisors, whose sum is σ = 205865982. Its totient is φ = 205865980.

The previous prime is 205865951. The next prime is 205865987. The reversal of 205865981 is 189568502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 126922756 + 78943225 = 11266^2 + 8885^2 .

It is a cyclic number.

It is not a de Polignac number, because 205865981 - 2⁶ = 205865917 is a prime.

It is a super-2 number, since 2×205865981² = 84761604266184722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205865987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102932990 + 102932991.

It is an arithmetic number, because the mean of its divisors is an integer number (102932991).

Almost surely, 2^205865981 is an apocalyptic number.

It is an amenable number.

205865981 is a deficient number, since it is larger than the sum of its proper divisors (1).

205865981 is an equidigital number, since it uses as much as digits as its factorization.

205865981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 172800, while the sum is 44.

The square root of 205865981 is about 14348.0305617182. The cubic root of 205865981 is about 590.4659548092.

The spelling of 205865981 in words is "two hundred five million, eight hundred sixty-five thousand, nine hundred eighty-one".