Königsberg Bridge Problem
The Königsberg bridges cannot all be traversed in a single trip without doubling back. This problem was solved byEuler, 
and represented the beginning of Graph Theory.
References
Bogomolny, A. ``Graphs.'' http://www.cut-the-knot.com/do_you_know/graphs.html. Chartrand, G. ``The Königsberg Bridge Problem: An Introduction to Eulerian Graphs.'' §3.1 in Introductory Graph Theory. New York: Dover, pp. 51-66, 1985. Kraitchik, M. §8.4.1 in Mathematical Recreations. New York: W. W. Norton, pp. 209-211, 1942. Newman, J. ``Leonhard Euler and the Königsberg Bridges.'' Sci. Amer. 189, 66-70, 1953. Pappas, T. ``Königsberg Bridge Problem & Topology.'' The Joy of Mathematics. San Carlos, CA: Wide World Publ./Tetra, pp. 124-125, 1989.
- Stirling Set Number
- Stirling's Finite Difference Formula
- Stirling's Formula
- Stirling's Series
- Stirrup Curve
- Stochastic
- Stochastic Calculus of Variations
- Stochastic Group
- Stochastic Matrix
- Stochastic Process
- Stochastic Resonance
- Stokes Phenomenon
- Stokes' Theorem
- Stolarsky Array
- Stolarsky-Harborth Constant
- Stolarsky's Inequality
- Stomachion
- Stone Space
- Stone-von Neumann Theorem
- Stopper Knot
- Straight Angle
- Straightedge
- Straight Line
- Straight Polyomino
- Strange Attractor