A Graph Theory Interpretation of the Sum of the First n Integers
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A complete graph on 
vertices has 
edges. This number is also the sum of the first 
integers, as shown here: the complete graphs are built up by adding one vertex at a time, and the colors show that the 
vertex adds edges, thus showing visually that 
.
Contributed by: Aaron Dunigan AtLee (March 2011)
After work by: J. DeMaio and J. Tyson (see citation above)
Open content licensed under CC BY-NC-SA
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Details
This Demonstration was suggested by the following article:
J. DeMaio and J. Tyson, "Proof without Words: A Graph Theoretic Summation of the First Integers," The College Mathematics Journal, 38, 2007 p. 296.
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