# What number is missing?

This is a sequence, that if transformed correctly, gives a sequence that is easily recognized by experts in a particular field of science.

There is a number missing, though. Can you help?

57, 86, __, 115, 112, 144, 100, 141, 173, 129, 170, 202, 131, 158, 199, 231, 160, 187

Hint:

@elias found out that it is chemistry. It is not related to atomic numbers, and is not directly related to the elements- you do not have to knw them to solve this.

• and what's that particular field of science? – A J Jun 18 '16 at 6:49
• Sorry. You have to guess it.. (Here's a hint: tables) – ev3commander Jun 18 '16 at 11:46
• @ev3commander I tired running program for equal subset sum problem (Computer Science), no success, yet. – ABcDexter Jun 18 '16 at 13:34
• Actually, the hint should be table, not tables. Also, it's not CS – ev3commander Jun 18 '16 at 14:32
• perhaps it is now time to add another hint or answer the question – A J Jun 20 '16 at 11:51

The numbers are orbital shells in order of filling converted from base 29 to base 10. They are: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d. (Looks like my source didn't have 5f and 6d, sorry, just edited it in) So, the missing number is 83 Source: LinkLink 2

• I think "20" is a typo for "29" here. (And ... seriously, dude, base 29? I mean, I understand how you chose it, but that's one seriously weird way to represent them.) – Gareth McCaughan Jun 21 '16 at 2:07
• And this is not directly related to the hint - tables. Also, the electronic configurations are 1s² 2s² ... not only 1s and 2s. – dryairship Jun 21 '16 at 11:57
• @Hackerdarshi The hint was for the field, not the answer. I thought I made that obvious – ev3commander Jun 21 '16 at 19:28

Based on the hints (related to a table, not yet discovered objects), I would say this has to do something with

the periodic table.

However, it is definitely not about

atomic numbers. At least not directly, as some of the numbers in the question are way too big to be a valid atomic number of currently known chemical elements. Maybe that's where the transformation comes into the picture?

• Yes, it's chemistry, and no, it doesn't directly have to do with elements, and not in any way connected with atomic numbers. – ev3commander Jun 19 '16 at 13:12