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 A222010 Dimensions of spheres that admit continuous multiplications with unit element. 1
 0, 1, 3, 7 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Adams's (1960) Hopf invariant one theorem states that S^0, S^1, S^3, S^7 are the only spheres that are H-spaces, i.e., that admit continuous multiplications with unit element. This is related to the fact that nontrivial cross products only exist in vector spaces of 3 or 7 dimensions. [Jonathan Vos Post, Feb 09 2013] LINKS J. F. Adams, On the non-existence of elements of Hopf invariant one, Ann. Math., 72 (1960), 20-104. Peter F. McLoughlin, When does a cross product on R^{n} exist?, arXiv:1212.3515 [math.HO], 2012-2013. Wikipedia, H-space Wikipedia, Hopf invariant one FORMULA a(n) = 2^n - 1 for n = 0, 1, 2, 3. a(n) = A222011(n) - 1. EXAMPLE 0, 1, 3, 7 are members because multiplications on S^0, S^1, S^3, S^7 are defined by regarding them as the unit spheres in the real, complex, quaternion, and Cayley numbers, respectively. CROSSREFS Cf. A222011. Sequence in context: A157596 A111316 A297530 * A152590 A261873 A293525 Adjacent sequences:  A222007 A222008 A222009 * A222011 A222012 A222013 KEYWORD nonn,fini,full,nice AUTHOR Jonathan Sondow, Feb 06 2013 STATUS approved

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Last modified September 18 20:19 EDT 2020. Contains 337173 sequences. (Running on oeis4.)