For each calculation, you are kindly asked to enter a captcha code as it is shown in this image. The reason is: we can give away free calculations with guaranteed correctness only to real humans. Therefore, we need to verify that you are a human and not a computer. This website has been inundated with requests for calculations from remote servers instead of people, which caused a high load. By forcing this captcha on you, we make sure we can keep offering you this free service.
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Here are a few hints in case the text is illegible: