this is my number sequence:

/ - / - 1 - 2 - 7 - 6 - ?

This riddle has somtething to do with equilateral triangles
Good luck and have fun :)

PS: please tell me if this is too broad,
this is my first number-sequence level

  • $\begingroup$ Are these dashes intentional? Are they part of the puzzle? If not, what do they mean? $\endgroup$
    – Wais Kamal
    Nov 7 '18 at 15:19
  • $\begingroup$ @WaisKamal They are part of the puzzle. They mean as you might think idk/not there/undefined $\endgroup$
    – user52327
    Nov 7 '18 at 15:24
  • $\begingroup$ Another question, is this the start of the sequence or just a part of it? $\endgroup$
    – Wais Kamal
    Nov 7 '18 at 15:26
  • $\begingroup$ @WaisKamal This is the start, mark a '1' over the first slash if you like $\endgroup$
    – user52327
    Nov 7 '18 at 15:26
  • $\begingroup$ @WaisKamal wait ... did you mean with dash the hyphens or the slashes? Because i meant the slashes with idk/not there/undefined, the hyphons are just to seperate $\endgroup$
    – user52327
    Nov 7 '18 at 16:30


The answer is:

impossible? (or '/' as per the question)


The constructed shapes must only have acute interior angles, it is impossible to make a heptagon with equilateral triangles

An explanation is given by this picture


Original Guess

I think the answer is:


Each number is in the sequence correlates to:

The number of equilateral triangles required to build a shape which has the corresponding number of sides:

1 and 2-sided shapes with straight edges don't exist in 2D, hence the lack of values.
A 3-sided shape takes 1 triangle (it's already a triangle :P )
A 4-sided shape takes 2 triangles (a diamond)
A 5-sided shape takes 7 triangles (an irregular pentagon)
A 6-sided shape takes 6 triangles (a regular hexagon)
A 7-sided shape can be made with 8 triangles, the next number in the sequence

Like so:

Triangle Solution

  • $\begingroup$ You're close but not right. $\endgroup$
    – user52327
    Nov 9 '18 at 8:49
  • $\begingroup$ Any closer? I'm outta answers if this one is wrong $\endgroup$
    – Dmihawk
    Nov 9 '18 at 8:54
  • $\begingroup$ I can tell you: the forms you drawed, except the last one are all correct $\endgroup$
    – user52327
    Nov 9 '18 at 8:56
  • $\begingroup$ So my new assumption is wrong? $\endgroup$
    – Dmihawk
    Nov 9 '18 at 8:57
  • $\begingroup$ the last shape is incorrect. your logic has a fault $\endgroup$
    – user52327
    Nov 9 '18 at 8:59

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