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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
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
KEYWORD
nonn,nice
AUTHOR
STATUS
approved

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