Hey everyone. I make a Facebook page in which we learn Kanji from a viewpoint of a mathematic graduate cause I am one myself. It's all in Indonesian, though. Here is the page:
https://facebook.com/ShuugakuHitoKaraKanjiNiNarau/This is the first image which I uploaded there:
The Kanji for 1, 2, and 3 are similar to their Roman numeral (I, II, and III) rotated 90 degrees (一, 二 and 三).