Hojoo Lee (Korea) has compiled up number theory problems from elementary number theory and uploaded the draft of PEN Problems Book in 2005 on his webpage.
After that,he has completely stopped working on this project. However, Project PEN is not dead. Since 2006, Peter Vandendriessche from Belgium is doing excellent work on PEN as the main author of PEN Problems Book.
In early 2007, Peter created a brand new site PEN Website. PEN staffs includes Peter, darij grinberg, Hawk Tiger, Ilthigore, Tiks, ZetaX, ideahitme. In July 2007, we’ve moved to MathLinks, which is the world’s best Math online community. Project PEN has its supporting site at Mathlinks.
This Biweek problems project began here. With Andrei Frimu (Moldova) and Yimin Ge (Austria), Hojoo created the PEN Team. He also opened a Project PEN group on facebook. (Anyone who loves number theory is welcome!) We weblished PEN extended as an extension of PEN Problems Book.
Around August, Cosmin Pohoata (Romania), Daniel Kohen (Argentina), Ofir Gorodetsky (Israel), David Kotik (Canada), Ho Chung Siu (Hong Kong), Soo-Hong Lee (Korea) joined the PEN Team. We weblished Problems in Elementary Number Theory 1 [ 2008 ] No. 1.
We are glad to announce you that Editors-in-Chief ‘09 are
Daniel Kohen (Argentina)
Cosmin Pohoata (Romania)
Peter Vandendriessche (Belgium)
Orlando Doehring (Germany) joined PEN team as the managing editor.
We appreciate it if you suggest challenging, interesting, beautiful or historical problems in elementary number theory by email or via the supporting website. We are very grateful to all contributors including
Prasad Chebolu, Orlando Doehring, Daniel Harrer, Arne Smeets, Ha Duy Hung, Tom Verhoeff, Tran Nam Dung, PEN staffs (Peter, darij grinberg, Hawk Tiger, Ilthigore, Tiks, ZetaX, ideahitme) & Valentin Vornicu.