Ed Pegg Jr., April 12, 2004
Using the set of symbols {1, ×, +} and parentheses, how many 1's does it take to represent 23? It turns out that eleven are needed. Surprisingly, the number 27 requires only nine.References:
N J A Sloane. Sequences A000001, A000792, A005245, A056792, A061373 in "The On-Line Encyclopedia of Integer Sequences." http://www.research.att.com/~njas/sequences/.
Stephen Wolfram, Operator representations, NKS|Online, http://www.wolframscience.com/nksonline/page-916.
Mathematica
Code:
A notebook that generates all the images and sequences above can be found as item 5175 at the Mathematica Information Center.
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