From the history of maths
Carl Friedrich Gauss
At 19 he showed that a regular 17-sided polygon can be drawn with ruler and compass, and reportedly wanted one on his tombstone.
The story of him adding 1 to 100 in seconds is probably embellished, but he called quadratic reciprocity his “golden theorem” and proved it several ways.
Christian Albrecht Jensen, Public domain, via Wikimedia Commons
Where you’ll meet Carl Friedrich Gauss here
They turn up beside problems and lessons on these topics.
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D. R. Kaprekar
A schoolteacher who loved number curiosities. Take a four-digit number (not all digits the same), sort its digits largest-first and smallest-first, subtract, and repeat.
You always reach 6174 within seven steps, and then you stay there.
Kaprekar’s constant
No portrait of D. R. Kaprekar survives, so we show the mathematics instead.