Ah, found the story. Wasn’t quite as I remembered. (Search for “wrong number”.)
https://arthurjensen.net/wp-content/uploads/2014/06/Speed-of-Information-Processing-in-a-Calculating-Prodigy-Shakuntala-Devi-1990-by-Arthur-Robert-Jensen.pdf
Ah, found the story. Wasn’t quite as I remembered. (Search for “wrong number”.)
https://arthurjensen.net/wp-content/uploads/2014/06/Speed-of-Information-Processing-in-a-Calculating-Prodigy-Shakuntala-Devi-1990-by-Arthur-Robert-Jensen.pdf