I wanted to choose 3, 7, 22 or 227 because they are used when estimating PI, but some other students must have had the same idea.

我想选3、7、22或227，因为在估计圆周率时要用到它们，但其他一些学生肯定有同样的想法。

youdao

So z equals 7 -- this is the cut-off where, in fact, the sigma orbital is going to be higher in energy than the pi 2 p orbitals.

所以z等于7-这是分界点，实际上，sigma轨道能量,要比π2p轨道高。

麻省理工公开课 - 化学原理课程节选