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A222010
Dimensions of spheres that admit continuous multiplications with unit element.
1
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
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
KEYWORD
nonn,fini,full,nice
AUTHOR
Jonathan Sondow, Feb 06 2013
STATUS
approved