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A006481
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Euler characteristics of polytopes.
(Formerly M0533)
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1
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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; internal format)
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OFFSET
| 1,2
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REFERENCES
| H. Hadwiger and P. Mani, On polyhedra with extremal Euler characteristic, J. Combin. Theory, A 17 (1974), 345-349.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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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). - R. Stephan, Jun 07 2005
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MATHEMATICA
| a[n_] := Binomial[n-1, 2*Floor[(n-1)/4] + 1] + 1; Table[a[n], {n, 1, 29}] (* From Jean-François Alcover, Jan 23 2012, after R. Stephan *)
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CROSSREFS
| Very like A051920.
Sequence in context: A073528 A116067 A063685 * A118597 A083160 A123823
Adjacent sequences: A006478 A006479 A006480 * A006482 A006483 A006484
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KEYWORD
| nonn,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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