Step 1: Understanding the Concept:
The gaps between consecutive terms, 3, 5, 7, 9 (all subtracted), are consecutive odd numbers, and consecutive odd numbers follow the general formula \(2k+1\) for the \(k\)-th gap, starting at \(k=1\).
Step 2: Key Formula or Approach:
Write the gap between term \(k\) and term \(k+1\) as \(2k+1\), and use \(k=5\) to find the gap between the fifth and sixth terms directly, without listing every earlier gap first.
Step 3: Detailed Explanation:
Checking the formula against the known gaps: for \(k=1\), \(2(1)+1=3\), matching the drop from 53 to 50. For \(k=2\), \(2(2)+1=5\), matching the drop from 50 to 45. For \(k=3\), \(2(3)+1=7\), matching the drop from 45 to 38. For \(k=4\), \(2(4)+1=9\), matching the drop from 38 to 29.
For the gap between the fifth and sixth terms, \(k=5\): \(2(5)+1=11\).
So the sixth term is \(29 - 11 = 18\).
Step 4: Final Answer:
The missing number is 18.
\[ \boxed{18} \]