What is the pattern in the sequence 8,5,7,17,20,29,2?

Question

That's the whole question. My Chem teacher gave this as extra credit, and when nobody got it in the first 15 minutes or so, he said we were "overthinking" it. I don't think it is related to chemistry, just a "lateral thinking" exercise. Any ideas? Thanks!

Answer 1

There is no pattern. By thinking about it alone, you were overthinking it.

Answer 2

I haven't figured it out yet but my first thought was number of letters in something.  My second thought is that since it's chemistry, it has something to do with the periodic table.  I looked at the letters that correspond to the numbers and got

O B N Cl  Ca  Cu  He

Doesn't make any sense to me but maybe it will help.

Good luck !

Answer 3

I went straight to the periodic table also.

O B N Cl Ca Cu He

Although I cannot find any pattern among the elements.