The twenty-two cards of the tarot’s Major Arcana are numbered 0 through 21. That is not an accident. The deck was built in a culture that took the numbers from 0 to 21 seriously, and each Roman numeral on the card is doing work the modern reader sometimes ignores. 0 the Fool, 1 the Magician, 2 the High Priestess, all the way up to 21 the World. Each digit carries the same Pythagorean fingerprint it carries in a name.
Numerologists who also read tarot rarely treat the two traditions as rivals. They use one to gloss the other. The pictorial story of the card gives you the flavour. The numerological reduction of the card gives you the structural meaning. A reader who knows both can speak in stereo — the image saying one thing in metaphor, the number saying the same thing in arithmetic.
This works in part because both traditions came up in the same intellectual soil. Pythagoras, the Hermetic revival, the Kabbalah, the early decks — they share assumptions about the numbers one through nine. The tarot just chose to dramatise them with pictures.