There are actually lowercase-like 'oldstyle' forms of normal numbers with more pronounced ascenders and descenders, which is why some numbers like '5' in books sometimes dangle below the line. But the true capital numbers remain the domain of number maven Mavis Beacon.

"Mavis Beacon", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License

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There are actually lowercase-like 'oldstyle' forms of normal numbers with more pronounced ascenders and descenders, which is why some numbers like '5' in books sometimes dangle below the line. But the true capital numbers remain the domain of number maven Mavis Beacon.