205663981 has 2 divisors, whose sum is σ = 205663982. Its totient is φ = 205663980.

The previous prime is 205663949. The next prime is 205663987. The reversal of 205663981 is 189366502.

205663981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 204061225 + 1602756 = 14285^2 + 1266^2 .

It is a cyclic number.

It is not a de Polignac number, because 205663981 - 2⁵ = 205663949 is a prime.

It is a super-2 number, since 2×205663981² = 84595346161536722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205663987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102831990 + 102831991.

It is an arithmetic number, because the mean of its divisors is an integer number (102831991).

Almost surely, 2^205663981 is an apocalyptic number.

It is an amenable number.

205663981 is a deficient number, since it is larger than the sum of its proper divisors (1).

205663981 is an equidigital number, since it uses as much as digits as its factorization.

205663981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 77760, while the sum is 40.

The square root of 205663981 is about 14340.9895404745. The cubic root of 205663981 is about 590.2727657662.

The spelling of 205663981 in words is "two hundred five million, six hundred sixty-three thousand, nine hundred eighty-one".