1,2,4,8 과 1,3,7

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• The Scarcity of Cross Products on Euclidean Spaces
  
  • Bertram Walsh
  • The American Mathematical Monthly, Vol. 74, No. 2 (Feb., 1967), pp. 188-194
• Cross Products of Vectors in Higher Dimensional Euclidean Spaces
  
  • W. S. Massey
  • The American Mathematical Monthly, Vol. 90, No. 10 (Dec., 1983), pp. 697-701
• Parallelizability of Spheres

On the Non-Existence of Elements of Hopf Invariant One

• J. F. Adams
• The Annals of Mathematics, Second Series, Vol. 72, No. 1 (Jul., 1960), pp. 20-104