viewimage.php?no=24b0d769e1d32ca73ded83fa11d0283177940c12fe472eea84be02aa9a6012ac732043de33aaeeea601fd5d8ddacffdc42d91176e787bacff656d9f0d1560bcc516f58017300ab7bff89b7ccce8da9707c67575a2bda957014db83

an은 등차수열인데
교대급수 이후 처리가 안되네..