cotpi is a website meant for puzzle freaks. Puzzle enthusiasts can find a new puzzle every Sunday on this website.
Source of puzzles
One of the central objectives of this website is to provide as many original puzzles as possible to its readers. So, most puzzles are either orignal puzzles written by the author, or new puzzles derived from known puzzles. A few puzzles from folklore are also published from time to time when the author doesn't get enough time to spend with mathematical problems.
In the world of puzzles and mathematical problems, it is quite common to lift puzzles from various sources and share them with others while forgetting to give credit to the actual sources. This website, however, is trying to provide due credits to each source on which a puzzle on this website is based on directly or indirectly. Solutions to each puzzle is followed by a 'Credit' section that clearly specifies if it is an original puzzle or if it is based on an existing puzzle.
Source of solutions
Solutions to puzzles are contributed by the readers of the puzzle blog. Occasionally, the author of the blog adds his solutions if the solutions he had in his mind were not sent by any reader.
Every new puzzle that appears on the puzzle blog remains in unsolved state for at least 3 days. Solutions that have been verified and found to be correct within these 3 days are not published immediately. They are published 3 days after the puzzle appeared on the website. Solutions to puzzles which are older than 3 days are published as soon as they are verified.
In other words, a solution submitted to a puzzle is published 3 days after the puzzle was published or after it is verified, whichever is later.
Network with puzzles enthusiasts
There is an IRC channel for the readers of this website. There is also a Facebook page for this website. You can post messages to this page and interact with other puzzle freaks by clicking the 'Message' button just below the banner.