Earlier I wrote about remembering fractions of 6 due to influence of cricket. In the footnotes there, I mentioned also being good with number 7.
I remembered why I (subconsciously) know so many multiples and fractions of 7. It’s got to do with all those physics problems in high school.
Gravitational acceleration (g) near earth is 9.8m/s2. This can also be written as 7*7*2/10.
2 and 10 are easy to manoeuvre. 7 required me to calculate the fractions and multiples.
Since there were a lot of questions with g involved, I subconsciously memorised the frequent multiples and fractions. Now, decades later, I still (subconsciously) remember a fair number of them without having to bother with the calculation.