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Search: id:A009117
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| 1, -2, 8, -32, 128, -512, 2048, -8192, 32768, -131072, 524288, -2097152, 8388608, -33554432, 134217728, -536870912, 2147483648, -8589934592, 34359738368, -137438953472, 549755813888, -2199023255552, 8796093022208, -35184372088832, 140737488355328, -562949953421312
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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Ghislain R. Franssens, On a Number Pyramid Related to the Binomial, Deleham, Eulerian, MacMahon and Stirling number triangles, Journal of Integer Sequences, Vol. 9 (2006), Article 06.4.1.
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LINKS
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INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 171
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FORMULA
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1 followed by (-4)^n /2.
a(n)=Sum_{k, 0<=k<=n} A086872(n,k)*(-3)^(n-k). - Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Aug 17 2007
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MATHEMATICA
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Cos[ x ]^2 (* Even Part *)
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CROSSREFS
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a(n) = (-1)^n*A004171(n-1).
Sequence in context: A099752 A081294 A004171 this_sequence A160637 A150829 A155084
Adjacent sequences: A009114 A009115 A009116 this_sequence A009118 A009119 A009120
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KEYWORD
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sign,easy
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AUTHOR
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R. H. Hardin (rhhardin(AT)att.net)
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EXTENSIONS
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Signs added and formula corrected Mar 15 1997 by Olivier Gerard.
More terms from Olaf Voss (richyfourtythree(AT)yahoo.com), Feb 13 2008
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