Triangle Counting
Given rods of length 1, 2, ..., 
, how many distinct triangles 
can be made? Lengths for which
obviously do not give triangles, but all other combinations of three rods do. The answer is
The values for
, 2, ...are 0, 0, 0, 1, 3, 7, 13, 22, 34, 50, ... (Sloane's A002623). Somewhat surprisingly,this sequence is also given by the Generating Function
References
Honsberger, R. More Mathematical Morsels. Washington, DC: Math. Assoc. Amer., pp. 278-282, 1991. Sloane, N. J. A. SequenceA002623/M2640in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.
- ISBN
- I-Signature
- Island
- Isobaric Polynomial
- Isochronous Curve
- Isoclinal
- Isocline
- Isoclinic Groups
- Isodynamic Points
- Isoenergetic Nondegeneracy
- Isogonal Conjugate
- Isogonal Line
- Isogonic Centers
- Isograph
- Isohedral Tiling
- Isohedron
- Isolated Point
- Isolated Singularity
- Isolating Integral
- Isometric Latitude
- Isometry
- Isomorphic Graphs
- Isomorphic Groups
- Isomorphic Posets
- Isomorphism