With enough interest being shown in these special numbers, maybe the Charlton catalog will eventually have a premium for just the general category of a special number , eg Pi 3141592 or e 2718281 (truncated decimal places of course). As a collector, I would pay a premium for notes such as these. However, I may be one of a few as they may only appeal to the mathematically inclined although I would think they have a greater appeal than birthyear notes which have their own designation in Charlton's.