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 A006481 Euler characteristics of polytopes. (Formerly M0533) 3
 1, 2, 3, 4, 5, 11, 21, 36, 57, 127, 253, 463, 793, 1717, 3433, 6436, 11441, 24311, 48621, 92379, 167961, 352717, 705433, 1352079, 2496145, 5200301, 10400601, 20058301, 37442161 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 H. Hadwiger and P. Mani, On polyhedra with extremal Euler characteristic, J. Combin. Theory, A 17 (1974), 345-349. See p. 346. FORMULA Numbers suggest that for n not divisible by 4, a(n) = C(n, [n/2]) + 1 and C(n, [(n-1)/2]) + 1 otherwise (see A051920 and A037952+1). - Ralf Stephan, Jun 07 2005 MATHEMATICA a[n_] := Binomial[n-1, 2*Floor[(n-1)/4] + 1] + 1; Table[a[n], {n, 1, 29}] (* Jean-François Alcover, Jan 23 2012, after Ralf Stephan *) CROSSREFS Very like A051920. Cf. A320996. Sequence in context: A073528 A116067 A063685 * A118597 A083160 A123823 Adjacent sequences: A006478 A006479 A006480 * A006482 A006483 A006484 KEYWORD nonn,nice AUTHOR N. J. A. Sloane STATUS approved

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Last modified April 14 18:28 EDT 2024. Contains 371667 sequences. (Running on oeis4.)