What's the next number in the following sequence?

1, 3, 6, 7, 9, 11, 13, 14, 18, 21, 23, 28, 31, ___, ...

Hints will be released gradually - the first one is in the title.

Hint #2:

Depending on where you live, you may have never seen these numbers.


Never seeing these numbers is in fact an advantage, not a disadvantage.

Hint #3:

No math is involved (except for counting).

Hint #4:

The human brain may not be enough. Ask Google or Wikipedia for help.

Final Hint:

How do you search using Google for a sequence that you've never seen, or even has never existed? Google is not powerful enough to find something non-existent for you. You need to search for something else.

  • 1
    $\begingroup$ From Hint 2: Does this mean that someone in a different geographical location to you would be unable to solve this 'with ease'? $\endgroup$
    – Inazuma
    Commented Jun 9, 2016 at 20:25
  • $\begingroup$ No, I believe it shouldn't matter. You may need the same kind of "help" anyway. $\endgroup$
    – user24855
    Commented Jun 9, 2016 at 20:27
  • $\begingroup$ Maybe a hint?.. $\endgroup$
    – nicael
    Commented Jun 10, 2016 at 10:25
  • $\begingroup$ @nicael updated :) $\endgroup$
    – user24855
    Commented Jun 10, 2016 at 12:01

3 Answers 3


Answer is:


Search Google for the remaining numbers in the sequence:


Which gives:

The labels of Interstate highways. With both sequences, one gets 1,2,3,4,5,6,7,8...

Image added:

List of numbers used in main US Interstate Highways

  • $\begingroup$ Your link doesn't seem to be working, just so you know. $\endgroup$ Commented Jul 30, 2023 at 21:55



When put into a $2$ by $n$ field, a pattern is formed. It's shown in the green section. The red parts are the next sections of the sequence. Black spots are numbers in the sequence. This is read as $1$ at the top, $2$ at the bottom, $3$ on the top and one to the right and so on. enter image description here

  • 2
    $\begingroup$ Hmm, I don't quite get it... :P This doesn't seem to work well with the hints. $\endgroup$
    – user24855
    Commented Jun 9, 2016 at 17:20
  • $\begingroup$ Right answer, wrong method, hah. It's worth noting your pattern only starts quite a few numbers in... $\endgroup$ Commented Jul 31, 2023 at 10:38

Well, I realize it could be weird, but still -


The assumptions are

Every ten numbers begin with ones which have $1$ and $3$ as the last digit, the further numbers differ
$1,?$ Hence, it would look that the next number should end with $3$

  • $\begingroup$ It's not that complicated :) $\endgroup$
    – user24855
    Commented Jun 9, 2016 at 15:30
  • $\begingroup$ @Pig You mean what, the rule is way easier? $\endgroup$
    – nicael
    Commented Jun 9, 2016 at 15:58
  • 1
    $\begingroup$ It does not involve any complicated mathematical analysis. $\endgroup$
    – user24855
    Commented Jun 9, 2016 at 16:06
  • $\begingroup$ @Pig Huh, ok then. $\endgroup$
    – nicael
    Commented Jun 9, 2016 at 16:07
  • $\begingroup$ Make sure you've seen those updated hints. $\endgroup$
    – user24855
    Commented Jun 9, 2016 at 16:08

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