205640509 has 2 divisors, whose sum is σ = 205640510. Its totient is φ = 205640508.

The previous prime is 205640507. The next prime is 205640527. The reversal of 205640509 is 905046502.

205640509 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 188293284 + 17347225 = 13722^2 + 4165^2 .

It is a cyclic number.

It is not a de Polignac number, because 205640509 - 2¹ = 205640507 is a prime.

Together with 205640507, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205640507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102820254 + 102820255.

It is an arithmetic number, because the mean of its divisors is an integer number (102820255).

Almost surely, 2^205640509 is an apocalyptic number.

It is an amenable number.

205640509 is a deficient number, since it is larger than the sum of its proper divisors (1).

205640509 is an equidigital number, since it uses as much as digits as its factorization.

205640509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10800, while the sum is 31.

The square root of 205640509 is about 14340.1711635531. The cubic root of 205640509 is about 590.2503093798.

The spelling of 205640509 in words is "two hundred five million, six hundred forty thousand, five hundred nine".