206509981 has 2 divisors, whose sum is σ = 206509982. Its totient is φ = 206509980.

The previous prime is 206509969. The next prime is 206510009. The reversal of 206509981 is 189905602.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 126765081 + 79744900 = 11259^2 + 8930^2 .

It is a cyclic number.

It is not a de Polignac number, because 206509981 - 2¹⁵ = 206477213 is a prime.

It is a super-2 number, since 2×206509981² = 85292744505240722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (206509181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 103254990 + 103254991.

It is an arithmetic number, because the mean of its divisors is an integer number (103254991).

Almost surely, 2^206509981 is an apocalyptic number.

It is an amenable number.

206509981 is a deficient number, since it is larger than the sum of its proper divisors (1).

206509981 is an equidigital number, since it uses as much as digits as its factorization.

206509981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 206509981 is about 14370.4551424094. The cubic root of 206509981 is about 591.0810220238.

The spelling of 206509981 in words is "two hundred six million, five hundred nine thousand, nine hundred eighty-one".