@lynnesbian My immediate thought when I saw this was "1st generation popular microprocessor", e.g. 8080, 6800, 6502, etc.

These days with 64 bit processors, the forbidden number would be 18,446,744,073,709,551,616 and I don't think Europe, let alone Switzerland, would have enough rails to hold that train(*)

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(* Yes I know that the length of that train would be over a million times the distance to Alpha Centauri and I doubt Swiss federal law would operate well at that distance)