6
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Start with

1

1 1

2 1

2 1 1 8

2 1 2 8

?

Your answer should explain what these numbers represent.

Hint 1:

See the new tag

Hint 2:

Look and say with Periodic Table

Hint 3

Fourth is Hydrogen Peroxide

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8
  • 1
    $\begingroup$ I always like sequences that start like other sequences and then veer off dramatically $\endgroup$ Oct 12 '21 at 13:34
  • $\begingroup$ For me a sequence is a one dimensional array of numbers. Here I see some numbers arranged in a two-dimensional-ish grid and a single 1 lying outside the grid. This is very unconventional sequence ... $\endgroup$
    – WhatsUp
    Oct 12 '21 at 14:28
  • 1
    $\begingroup$ One number is out of the blockquote. On purpose? $\endgroup$
    – msh210
    Oct 12 '21 at 14:37
  • $\begingroup$ Not particularly. Once the answer is in it will make sense. $\endgroup$
    – DrD
    Oct 12 '21 at 19:36
  • $\begingroup$ The only thought i had i put in answer. Any new hints? $\endgroup$
    – Morris
    Nov 3 '21 at 7:08
1
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I think the next in the sequence is:

Trioxidane (H2O3)

The first line 1 1 should be read as:

1 atom of element 1 (i.e., Hydrogen)

Then the second line 2 1 is read as:

1 atoms of element 1 = H2 (Hydrogen Gas)

For 2 1 1 8 we get:

2 element 1s and 1 element 8 = H20 (Water)

Then we progress to 2 1 2 8:

2 element 1s and 2 element 8s = H202 (Hydrogen Peroxide)

If we kept extending we would:

follow H2O3 with H2O4, then H2O5. Following the Hydrogen polyoxides in other words.

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1
  • $\begingroup$ I still don't understand what this sequence is. I mean I can see how it extends from the third term but why are the first two terms there? Amoz also seems to have made this point in the comments. $\endgroup$
    – hexomino
    Dec 7 '21 at 17:00
1
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It looks like next row should be

2 1 3 8

Explanation:

These are electron count of the elements in periodic table. Hydrogen have 1 electron, Helium have 2. Then new period starts. It build on helium (2 electrons in first orbit), and have 1,2,3...8 in second.

So next ones will be

2 1 3 8
2 1 4 8
2 1 5 8
and so on till 2 1 8 8

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1
  • 1
    $\begingroup$ I had a very similar thought about this, but why have '1' in the second position and not '2' in the fourth, or '8' in the fourth position and not '2' in the second...? $\endgroup$
    – Stiv
    Oct 24 '21 at 9:35

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