How many rectangles are there in a 8x8 chess board?
The geometry behind 1^3+2^3+...+n^3, see 6:00,    • 1^3+2^3+3^3+...+n^3 and its geometry  
Proof by induction,    • Prove by induction, Sum of the first ...   ,

a combinatoric problem, find the pattern, discrete math problem, number of rectangles on a checkerboard

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