I found an exciting article recently; it describes the calculating powers of Professor Craig Aitken.
I prepared a few more examples — this time illustrating how one approaches just writing the answer — one version below is marked with guidance, the other is unmarked.
After a little practice, the carries and subtractions become mental, allowing just the answer to be written.
I prove that, thanks to Wolfram Alpha, anyone can do all of this, and quicker yet — with a phone.
Dr. Aitken was both a mathematician and a mental calculator. His prowess is described in the first link below (about halfway down the page).
https://mathshistory.st-andrews.ac.uk/HistTopics/Mental_arithmetic/
And here’s a second link — well worth reading.
https://cowles.yale.edu/sites/default/files/files/pub/d17/d1750.pdf
https://www.mathpax.com/feed 
