So I (incited by some others) calculated the following
setprecision(15*10^5) x=big(9528)/10000; y=cos(x); ys=string(y); ys[306890:306931] "459423813195289597370437889596885962619893..."
Now this is somehow wrong…The correct sequence is:
In fact doing one newton-iteration with the first wrong number:
gives the desired result above, which I would have assumed however to be correct in the first place…
So what is going wrong here?