It’s the Friday Puzzle!


It’s that time again!  OK, here is the puzzle…..what number comes next in the sequence?

1    4    7    11    15    19

Clue: It is less than 19.

As ever, please do NOT post your answers, but do say if you think you have solved the puzzle 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.


68 comments on “It’s the Friday Puzzle!

  1. I know exactly how to find the next number now it is a matter of hunting for it.

  2. Quicker that I thought. The Clue was helpful really limiting the choices. I like this puzzle.

  3. Mike Hitchcock says:

    Shouldn’t have left the clue – I’d never have seen it without.

  4. Simon Taylor says:

    The clue is essential. Took a couple of minutes.

  5. I deal with numbers a fair bit… tensor calculus, differential geometry etc… these things always make my head hurt.

  6. Simon Taylor says:

    Numbers are your problem, Steve.

  7. Craig Morgan says:

    Got it in 3-4 minutes.

  8. Carl says:

    I think I’ve got it, but I’m a little confused. As far as I can tell, the next number in the sequence doesn’t HAVE to be less than nineteen, it could be one of several options. If it HAS to be less than 19, then, by my figuring, the third number in the sequence should be three, not 7.

    Or have I just got the wrong rule?

  9. photon says:

    Couple of minutes, although to be consistent with the clue some of the earlier numbers in the sequence should be different.

  10. I agree. If we said that in all cases where there’s a choice that one goes for the lowest option it would make it more logical. So, next question – how long does the sequence go on before you can’t continue it?

    • tort says:

      it’s a sequence, it doesn’t have to be a unique sequence. The point is that there is only one number under 19 that fulfils the conditions.

  11. Tom Pedersen says:

    I’m reasonably sure I found the same answer as Carl. Noticed the pattern early on, found what I thought was the answer, double checked it an found that the 7 did not completely match the pattern as defined by the clue.

    So, if is the answer, I got it in under 5 minutes. Might continue to look.

  12. I’m certain I have solved it. It took me 2-3 minutes.

  13. Anonymous says:

    30 secs but I agree with Carl

  14. Christy says:

    Im the beginning there was Carl. Now I can’t think of anything else.

  15. Toon says:

    About 30 seconds to one minute.

  16. Caroline says:

    Really nice puzzle. Clue helpful. A couple of mins

  17. Anonymous says:

    Got it but it doesn’t travel well…

  18. SofARMaths says:

    Woops. Anonymous was me. Hit enter too early!

  19. Seconds to work out the sequence, a few more to find the number. I may have seen this one before. I’m not usually that quick.

  20. Lazy T says:

    It’s not really a sequence is it? It’s some arbitrary choices in a row.
    10 secs

  21. for the first time ever – i think ive got the answer! cant wait til monday to see how monumentally wrong i am (again)! haha

  22. Nicky Brunger says:

    I believe I have the answer. In fact I have two possibles, but am working on the premise that the correct one is the lower of the two. It took 5 mins or so.

  23. A Nusol says:

    0.12393402 seconds this time.

  24. Mathlete says:

    instead of 19 why not 13?

  25. In less than a minute I found one solution, but my definitons are loose. ie it doesn’t have to start with 1, 4 (and as Mathlete says it could be 13 instead of 19) – and there are answers above 19 I’ve found too!

  26. James Ernst says:

    Got it in about a minute.

  27. John Nevill says:

    I’ve been baffled by one of these in the past that ran in the same vein. It made my brain hurt. Thankfully I am on the lookout for them now so this one only took a minute to solve.

  28. danny says:

    45 seconds

  29. Waldo says:

    2 hrs, 12 min. (Including time off to run a marathon and smoke 2 cigarettes.)

  30. Anonymous says:

    Anyone else feel like we’re not really getting puzzles anymore, just math problems? Could do with changing it up a bit, getting bored now…

  31. FPC Craig says:

    I have what seems to be a correct answer, but I can’t use that answer and the given sequence to infer deterministic rules for constructing the sequence. So I’m either wrong or disappointed (or missing a key detail of the given sequence).

  32. M says:

    This one is slightly different

    1 2 7 12 13 14 17 101 31 21 22 27 77 207

  33. Nick says:

    Here’s my variation, for which the series is unique:
    1 4 3 11 15 13 __
    I think this is what many of the other commenters were getting at.

    • James says:

      Yes. We’ve clearly all got the same answer and reason, but the clue actually forces you to go for an answer that’s less consistent with the rest of the sequence than one you might otherwise choose. For me, it makes more sense if either the sequence is as you say, or the answer is greater than 19.

    • duckfish says:

      i think we got the same reason, not really math-related

    • duckfish says:

      I think I got it, if my guess is correct, this puzzle is amusing…..when the solution first came to my mind, i thought it is ridiculous but when I wrote it down, it proved my hypothesis!
      Here is my variation

      the limitation is nessesary
      2 5 3 8 12 16 13 ____ 24 28………

  34. Doug says:

    Cute. Got it in a few minutes.

  35. katie k says:

    I got the pattern immediately (I guess my brain is just working that way today) and it just took a few more seconds to figure out the right number. I think the clue probably helped.

  36. Caroline says:

    If we have got the right idea then definitely 13 would replace 19. May be we haven’t. Surely RW wouldn’t have made a mistake?

  37. Laith says:

    I may be completely missing something here (very likely) but if you are going and changing numbers in the sequence then it isn’t really the same sequence or same rules.

    That said I’ve never been good at this sort of puzzle.

  38. dharmaruci says:

    i do not believe numbers have “sequences” that they can be put in. numbers want to be free, and i for one will not attempt to ensalve them

  39. Chrissie says:

    I think the reason not 3 or 13 used is to make a sequence that increases. That would be the puzzle to which there might be more than one answer. The clue is a clever way of both ensuring only one answer and also being a pointer to how to solve it (usually the sole purpose of a clue). Some commenters have too pedantic and narrow-minded an approach to these puzzles which as well as being annoying, portrays them as boring “wet blankets”. (In my opinion)

  40. .mau. says:

    today I managed to do it. As for the not univocal solution, the simplest thing would have been to use every time the least number under the rule.

  41. with the clue, 2 minutes. without the clue would have been difficult

  42. Beaky says:

    Thought for 10 secs, then a minute to check…
    “easy” when you think about it correctly.

  43. Bert says:

    About a minute. I’m curious as to why you chose 7 and (instead of 3) and 19 (instead of 13). You wouldn’t have had to point out that the answer would be less than 19, because order wouldn’t have mattered. Unless you wanted to throw us off with the fact that most of the numbers are separated by 4.

  44. BADRU says:

    its way to simple…..

  45. Mushu Friend says:

    Everyone seems to think that they have the answer, but no one has posted their answer. Seems noone wants to run the risk of being wrong. — Hmmmm, interesting!

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