Melody

Thanks very much Tiggsy, makes perfect sense.  

Is this your way of saying thank you?

Thanks Heureka :)

The pic is blocked for me and I cannot unblock it.  It is probably visible on the answer tab.

Alan has also been having this problem a lot lately.    

Thanks very much Tiggsy,

I have updated my pic to display what you have said.  

That is what it appears to be from the graph.

Of course it could be  4.99 or 4.001 rather than 4 but    [-5,4]  is close and probably correct.

mmm

If the maths I have presented above is correct I do not see how this could work because you would be left with some primes example 37 that do not have a pair.

Maybe there is something wrong with my logic that  S = 100!*100!

I am not doubting your output but it does not make sense to me.

Maybe another mathematician will comment.

There is some simple circle geometry formula for this.

I am pretty sure I have seen Heureka use it.

You need to find another side first using the Sine rule.

then use the are of a triangle formula    A=1/2 ab sinC