· The numbers 1, 2,..... ,20 are written on a blackboard. It is permitted to erase any two numbers a and b and write the new number ab + a + b. Which number can be on the blackboard … · The numbers 1 1 to 2025 2025 are written on a blackboard and the following process is repeated for as long as there are enough numbers left: Three numbers are chosen. The largest two … 一、黑板粗体 (Blackboard bold) \mathbb实际上指的是 黑板粗体 (Blackboard bold)，在原先的字母基础上多了一些特定的线条，所以有时候也被称为 双线体 (double struck)。 黑板粗体一般是在数学中拿 … · Young authors (and some older ones) seem to prefer blackboard bold to plain bold for the standard number systems (and/or they pick it up by osmosis on web sites such as this one), and … · Does anyone know a good resource (preferably pictures) that illustrates a conventional way to write the special sets symbols, i.e. $\\mathbb{N,Z,Q,R,C}$ etc., by hand? In the first post of the thread "Cardinal number subtraction", Cardinal number subtraction there is a symbol for some kind of set which looks like this: $\\Bbb P$ I am familiar with symbo...
