'Yutori education' a Japanese education policy, was in the news several years ago, and in those days, the children were taught that the value of Pi was 3.14 or simply 3 for hand calculation. Pi (is the strange number that) cannot be obtained by dividing any integer by any other integer, and the challenge to find more digits of Pi has been continued since ancient times. In the 17th century BC, Egyptian book described that an area of square with side length of 8/9 of circle diameter was equal to the area of circle. The value of Pi was 3.16049治柴治柴, and the error was within 1 %. After that, Archimedes derived 223/71<Pi<22/7 by calculating the perimeters of circumscribed and inscribed polygons. Mathematicians challenged to find more digits of Pi by using this polygonal algorithm until 16th century, and Ludolph van Ceulen, a Dutchman, reached 35 digits of Pi in 1630. Yet we can instantly find 50 digits of Pi on Keisan online calculator and cannot help but thinking about Ludolph who dedicated his 70 years life to calculating 35 digits of Pi.