How long till Halley's Comet returns?
JavaScript (Node.js), 74 bytes

n=&gt;Buffer(&quot;BKMMOMOMMLMKMMOMOMNKLKLMKLKIKKJHJKJIEDDE&quot;).every(c=&gt;(n-=c)&gt;0)-n

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Commented
n =&gt;              // n = input year
  Buffer(         // build a buffer consisting of
    &quot;BKMM...EDDE&quot; // the year deltas encoded as ASCII codes
  )               // 'B' -&gt; 66, + 'K' (75) -&gt; 141, etc.
  .every(c =&gt;     // for each value c in there:
    (n -= c)      //   subtract c from n
    &gt; 0           //   and go on while the result is positive
  )               // end of every(), which yields false
  - n             // return -n