APL will be 50 years old in November 2016 (50 years from 1966-11-27 15.53.58, to be exact), and it remains unsurpassed in manifesting Kenneth E. Iverson's five important characteristics of notation: 
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<ul>
  <li>ease of expression</li>
  <li>suggestivity</li>
  <li>subordination of detail</li>
  <li>economy</li>
  <li>amenability to proof</li>
</ul>
These characteristics are demonstrated by working through 16 APL expressions. The material is approachable for beginners and yet thought-provoking for experts.
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One of the 16 expressions is a fast computation of the partition function without use of the Hardy-Ramanujan (1918) results.
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