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A191783 Numbers k such that the topological k-sphere has a unique differentiable structure up to diffeomorphism. 2
1, 2, 3, 5, 6, 12, 56, 61 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
Whether 4 is a term is an open question. - Andrey Zabolotskiy, Feb 02 2018
Except (possibly) for k=4, these are the numbers k such that A001676(k)=1. - Jeppe Stig Nielsen, May 22 2019
The list in Milnor's paper (p. 807, A358290) does not include the term 56 because it was only discovered later that it is actually a term of this list, see Wang & Xu, Theorem 1.14. - Andrey Zabolotskiy, Nov 29 2022
Dimensions without exotic spheres. - Charles R Greathouse IV, Dec 22 2022
LINKS
Brady Haran and Ciprian Manolescu, The Puzzling Fourth Dimension (and exotic shapes), Numberphile video (2022).
John W. Milnor, Differential Topology Forty-six Years Later, Notices Amer. Math. Soc. 58 (2011), 804-809.
Guozhen Wang and Zhouli Xu, The triviality of the 61-stem in the stable homotopy groups of spheres, Annals of Mathematics, 186 (2017), 501-580; arXiv:1601.02184 [math.AT], 2016-2017.
CROSSREFS
Sequence in context: A125877 A118787 A359668 * A358290 A098930 A075372
KEYWORD
nonn,more,hard,nice
AUTHOR
N. J. A. Sloane, Jun 25 2011
EXTENSIONS
Definition rewritten by Jeppe Stig Nielsen, May 22 2019
The term a(7) = 56 inserted by Andrey Zabolotskiy, Nov 27 2022
STATUS
approved

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Last modified June 16 14:12 EDT 2024. Contains 373430 sequences. (Running on oeis4.)