OEIS(数列) http://oeis.org/
Generic two integer variable equation solver(ax² + bxy + cy² + dx + ey + f = 0 的整数解) https://www.alpertron.com.ar/QUAD.HTM
https://webdemo.myscript.com/
https://csacademy.com/app/graph_editor/
SAM Drawer https://yutong.site/sam/