I had one slightly eccentric teacher who decided that the 25 and 125 times table were also necessary. While I don't know about necessary, I've definitely used t

I had one slightly eccentric teacher who decided that the 25 and 125 times table were also necessary. While I don't know about necessary, I've definitely used that knowledge (possibly more useful to think of them as the one-quarter and one-eighth times tables with a shift). 16 would have also been useful for mi/km conversion and hex/dec conversion.