I think you're referring to the "strong law of small numbers", as in this excellent article by Guy [1]. But the idea is the same --- so very frequently, pattern

I think you're referring to the "strong law of small numbers", as in this excellent article by Guy [1]. But the idea is the same --- so very frequently, patterns that hold for even the first several numbers eventually fail to continue. [1]: https://www.maa.org/sites/default/files/pdf/upload_library/22/Ford/Guy697-712.pdf https://www.maa.org/sites/default/files/pdf/upload_library/2...