Monthly Archives: March 2009

Read wrote Wright… Graph Theorists playing with words

Frank Harary, Oberwolfach (1972)

I was going through the first chapter of the book Graphical Enumeration by Frank Harary and Edgar M. Palmer when I chanced upon this perplexing footnote:

Read wrote Wright that both Read [R2]1 and Wright [W3]2 were wrong. So Read and Wright wrote a joint erratum [RW1]3 to set things right. This may be wrong since Wright asserts that Wright wrote Read first.

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  1. [R2] R.C. Read, The number of k-colored graphs on labelled nodes, Canad. J. Math. 12, 409–413 (1960).
  2. [W3] E.M. Wright, Counting coloured graphs, Canad. J. Math. 13, 683–693 (1961).
  3. [RW1] R.C. Read and E.M. Wright, Coloured graphs: A correction and extension, Canad. J. Math. 22, 594–596 (1970).

Solving Project Euler Problems 161 (Trominoes Tiling) and 185 (Number Mind) with ZDDs

Some months ago, I was re-introduced to Project Euler (PE) through the blogosphere. I had visited that site before, but had been left unmotivated by the first dozen or so problem statements that I read — neither the programming nor the math involved anything new or challenging. Only in the past few months, when I attempted to crack some of the harder nuts, did I realize how interesting many PE problems could be — requiring a neat algorithm (or invoking a crucial theorem) for an efficient solution. Continue reading