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A006482
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Euler characteristics of polytopes.
(Formerly M1357)
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0
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1, 1, 0, 2, 5, 9, 14, 20, 69, 125, 209, 329, 923, 1715, 3002, 5004, 12869, 24309, 43757, 75581, 184755, 352715, 646645, 1144065, 2704155, 5200299, 9657699, 17383859, 40116599
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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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>3, a(n) = C(n, [n/2])-1 if (n mod 4)=0 or 1 and C(n, [n/2]-1)-1 otherwise. - R. Stephan, Jun 07 2005
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PROG
| (PARI) a(n)=if(n<3, (n==0||n==1), if(n<4, 2, -1+if(n%4==0||n%4==1, binomial(n, n\2), binomial(n, n\2-1)))) /* (from R. Stephan) */
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CROSSREFS
| Sequence in context: A112873 A048093 A024669 * A191170 A191123 A152888
Adjacent sequences: A006479 A006480 A006481 * A006483 A006484 A006485
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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