If you read out the sequential digits of prime in such a way that you concatenate repeated digits until they make up a unique number, then presumably after an infinitely long process, you’ll create the set of cardinal numbers. To clarify:
At this stage (58 digits of pi), ‘7’ as a single digit hasn’t appeared yet, although 974 has. There’s 30 unique digits at this point.
Is there a name for this series? And if so, are there any interesting qualities of it, or generalisations that can be stated? Any limits on the proportion of cardinal numbers to the pi digits themselves?
I’m sure that the properties of pi have been researched to such an extent that I won’t be able to claim credit for naming the Ferris series, but that’s ok. Always nice to start the new year with an effort at profound thought!