It's the "pow(2,n)" part. It means that there are other versions of the function that take different arguments or different numbers of arguments, and you haven't provided enough information for it to figure out which one you wanted.
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pow(int a, int b, int c = 0);
pow(int a, int b, char c = "", int d = 0);
pow(x,y); //<-- would return ambigous call because compiler can't tell which function you want