Source: 1. Reader Hareendra Yalamanchili (later found at www.mathpuzzle.com for April 22.) 2. Reader Peter Bentley.
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ID Number: A008713 Sequence: 10,11,12,13,14,15,16,17,20,22,24,31,100,121,10000, 1111111111111111 Name: 16 in base 16-n. Example: 16 is 121 in base 3, so a(13)=121.