You need not to go up to _n / 2 to check whether a number is a prime.

Also, the hash is useless in this regard, the isprime and loop are sufficient to solve it!

OP solved it, closing

n is of type int so your cast to long long has no effect since it is downcasted to int again immediately. Thus you are only doing int-calculations in your return statement. Assign the long long to a new variable and it will work.

what could I be doing wrong?

Anything? If your code crashes, then your memory handling must be wrong.

tried it as well,
dont know why i still get the error message:

main.cpp:193:9: error: invalid operands to binary expression ('stringstream' (aka 'basic_stringstream') and 'X')
out << X();
~~~ ^ ~~~
/usr/include/c++/v1/ostream:191:20: note: candidate function not viable: no known conversion from 'X' to 'std::__1::basic_ostream &()(std::__1::basic_ostream &)' for 1st argument
basic_ostream& operator<<(basic_ostream& (__pf)(basic_ostream&));

Segfault.

I have the same problem, in c lang the last test crashes

in c language, i pass all the test but last one crashes,

i get this error code:
"Test Crashed
Exit code: 0
Signal code: 6"

what could i be doiing wrong?

Using RegEx should be cheating... ;)

Tests for 1 and 10 are successful, but test for 40 comes out wrong:
right answer is 1.4788962720000001 , but got: 1.4235528840000000.

any idea why can it be?