15
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This looks like a strange number sequence to me. Or is it?

1 2 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 20 21 22 23 24 25 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 ? ? ? ? ?

So what are the question mark numbers and why?

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1 Answer 1

25
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The next five terms in the sequence are:

46, 48, 49, 52 and 53

Because this sequence represents:

the atomic numbers of Periodic Table elements whose shortform symbol and English longform name begin with the same letter.

The sequence begins with 1 (Hydrogen=H), 2 (Helium=He), 3 (Lithium=Li), 4 (Beryllium=Be), 5 (Boron=B), 6 (Carbon=C), 7 (Nitrogen=N), 8 (Oxygen=O), 9 (Fluorine=F), 10 (Neon=Ne) but then skips element 11 which is Sodium (Na), before continuing with 12 (Magnesium=Mg) and so on...

The sequence also skips over elements 19 (Potassium=K), 26 (Iron=Fe), and then 47 (Silver=Ag), 50 (Tin=Sn) and 51 (Antimony=Sb).

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  • 3
    $\begingroup$ Maybe add in that you refer to the longform name in English. The shortform symbol is internationally uniform and even used in languages that do not use the latin alphabet. The longform name used in this puzzle is just the English word for the element. $\endgroup$
    – quarague
    Commented Mar 30, 2022 at 11:30
  • $\begingroup$ @quarague Done! :) $\endgroup$
    – Stiv
    Commented Mar 30, 2022 at 12:59
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    $\begingroup$ And also you needed to tag english (cc: @quarague) $\endgroup$
    – smci
    Commented Mar 31, 2022 at 0:32

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