The behavior of 9 in mathematics borders on the absurd.
Multiply any number by 9. Add the digits of the result. You get 9.
9 × 7 = 63. 6+3 = 9.
9 × 253 = 2277. 2+2+7+7 = 18. 1+8 = 9.
9 × 8,471 = 76,239. 7+6+2+3+9 = 27. 2+7 = 9.
This works for every number, without exception. Nine absorbs everything into itself, transforms it, and returns unchanged. No other single digit has this property.
— Read on x.com/thecurioustales/status/2025254391935369273
These strange math experiments illustrate how weirdly regular some of the patterns around us are.
