This is a number sequence puzzle. What is the next number in this sequence?

87, 135, 155, 212, 218, 292, 521, (522), (526), 636, 657,
758, (900), (980), 1037¹, 1104, (1110),   ̲ ̲ ̲?̲ ̲ ̲ ̲

                                            ¹ maybe?


Technically everything you need to solve this has been provided, but knowing what to do with it is another thing entirely.
  So hints will be added as time goes on.
If you aren't sure how to start, it will be helpful to know that the first number I gave you is the main part to address.
  But you'll probably need to rewrite it to solve it. And you'll likely need to find someone to explain it to you ....

  • 1
    $\begingroup$ Observation: 10,400 is tantalizingly close to the number of questions on this site (which recently hit 10,000). (There are more than 400 deleted questions, though). $\endgroup$
    – Deusovi
    Commented Jul 30, 2017 at 2:18
  • $\begingroup$ Are the parentheses and italicizations necessary to solve this, or do we only need the numbers themselves? $\endgroup$
    – benzene
    Commented Jul 30, 2017 at 2:24
  • 1
    $\begingroup$ You only need the numbers themselves to find the missing number. But if you figure out why some are bold, italicized, etc., you can determine which (if any) adornments the missing number needs. $\endgroup$
    – Rubio
    Commented Jul 30, 2017 at 2:29
  • $\begingroup$ may be something to do with periodic table $\endgroup$
    – user9174
    Commented Jul 30, 2017 at 4:57
  • 4
    $\begingroup$ Someone get this into the OEIS $\endgroup$
    – Stephen S
    Commented Jul 30, 2017 at 11:50

1 Answer 1


The next number seems to be...



The number sequence is actually the 18 pages in which Velociraptors were referenced in the popular webcomic xkcd, where a fear of them is a running theme:

87: Velociraptors; 135: Substitute; 155: Search History; 212: Brain; 218: Nintendo Surgeon; 292: goto; 521: 2008 Christmas Special; 522: Google Trends; 526: Converting to Metric; 636: Brontosaurus; 657: Movie Narrative Charts; 758: Raptor Fences; 900: Religions; 980: Money; 1037: Umwelt; 1104: Feathers; 1110: Click and Drag; 1249: Meteor Showers

As for the other clues

They seem to be bold when the raptor is in the actual title, italicized when it's only mentioned in the picture's title, in (parentheses) where it's only referenced indirectly or obscured somehow(?). (And in 1037, which was an April Fools gag where the comic changes based on the browser you're using, one result was Too Quiet where there's a silhouette that only might be a raptor.) 1249 will probably be in parentheses, since they're only indirectly referenced. As for 10,400, there are currently around 10,400 species of birds (source: Britannica) and birds have evolved from dinosaurs ('raptor' is also a bird of prey). But most are hardly threatening, unless you're Tippi Hedren. ;)

EDIT: Well, xkcd might actually mean 10,400: x(10)*k(1000)+cd(500-100). (Thanks, ffao!)

  • 1
    $\begingroup$ How did you get this answer? Do you know by heart all of the relevant numbers of the sequence? o_O $\endgroup$
    – ffao
    Commented Jul 30, 2017 at 11:43
  • 2
    $\begingroup$ Also, for 10400: it might be helpful to think Roman numbers. $\endgroup$
    – ffao
    Commented Jul 30, 2017 at 11:44
  • $\begingroup$ @ffao What else could you think of when hearing "things to be afraid of"? ;) $\endgroup$
    – Voo
    Commented Jul 30, 2017 at 11:49
  • 2
    $\begingroup$ @ffao Thanks for the tip!! "How did you get this answer" My chances of answering a riddle increase immensely when it's less mathy and more about pop culture. ;) $\endgroup$
    – Walt
    Commented Jul 30, 2017 at 11:58
  • 1
    $\begingroup$ Wow. I did not expect this to be solved with zero hints - very impressive. @ffao is entirely correct of course ("rewrite it to solve it") and I assume you know the meaning behind "you'll likely need to find someone to explain it to you" .... $\endgroup$
    – Rubio
    Commented Jul 30, 2017 at 14:09

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