Here is a series of numbers, starting with the number zero.  What is the hidden logic in the series and why can’t it be continued?

0, 1,  8,  10,  19,  90

As ever, please do NOT post your answers, but do say whether you think you have solved it and how long it took.  Solution on Monday.

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.


    1. There are two numbers which can continue this sequence.

      we are talking astronomical and microscopic though.

    2. I am looking forward to Monday. I looked through all the numbers on Wikipedia, and I still can’t find one that fits.

  1. Got it in a few seconds, surprisingly. Usually not too good at this type. Roland, I couldn’t find a number that matches the criteria you’re hinting at.

  2. Got it, but took about 2 minutes. Spent a long time pondering that gap of 71 at the end, which I guess is what the puzzle creator is hoping will happen.

  3. Had a good puzzle over it for a few minutes but got there. I’m not sure of the alleged continuation number referred to, unless we’re talking of a very small number.

  4. Took me about 10 seconds. I usually get stumped on these questions, but the answer to that one just jumped out at me.

  5. I’m stumped. It doesn’t appear to be mathematical (otherwise the series could continue), related to the number of letters / words in the question, Roman numerals, related to days of the week / months of the year, or even in an obscure base.

  6. Took me at least 5 minutes.
    Damn, those puzzles can be tough for people whose mother tongue is not english.

    1. It is more unusual than the leap from 19 to 90 but no more unusual than the leap from 0 to 1.

    2. If you consider that there are actually two “rules” at play here for getting the next number in the sequence and apply both of them, then the leap from 1 to 8 (and, equally, from 19 to 90) is the only way it can be.

  7. I think Richard finally taught me how to solve these puzzles 🙂
    I got it with the first idea I had to solve it. So less than a minute. Luckily I wasn’t thinking in Spanish!

  8. Ok, I got it now 😀 and I know why it can’t be continued 🙂
    Alain’s comment was very helpful 😀

    at first I though it was a date, 19 October 1990, but it turns out that it’s not 🙂
    (I’m allowed to say what is NOT the answer, right?)

  9. Yes, Alain’s comment was useful. Like others I struggled with many possible systems until I realized why that comment was helpful. I’ll be curious to know what very large or microscopic numbers people think come next.

  10. I’m guessing this is specific and science based as I’m stumped.
    I prefer puzzles where you can work out the answer rather than needing specific background knowledge.

  11. Finally got it! Very good. First looked at it when it was posted, couldn’t work it out, pondered it while at work, looked at it again when I got home. Still no idea. Looked at it again this morning and got it straight away. I guess I needed to sleep on it.

    1. well the romans didnt have 0 so it would go..

      1, 6 then finish

  12. 4-5 minuttes, Alain´s comment helped but the other comments helped me to continue the list forever (but it realy cant since it is not a real number as Nohj said! =)

  13. If instead of going from 8 to 10 we went from 8 to 2, then we’d get stuck in an infinite loop: 0182182182…

  14. I asked Richard for the answer at EMC…and he LIED(At least it doesn’t coincide with my answer)! Well wouldn’t have been any fun if he jut told us^^

  15. Mulled it over in my mind for a while then got it. Looking over the comments, particularly from Alain, Agata, and Hassan Selim, I am convinced I am right.

  16. In Italian, if the rule is enforced strictly: 0, 8, 80 stop
    If the rule is enforced loosely (meaning I can skip and look for the next best fit): 0, 8, 88, 800, 808, 888, 8800, 8808, 8888, 80008… and it does not end.

  17. By the same token, a loose implementation of the rule could stretch the Latin sequence to 1, 7, 1000, stop (I reckon)

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