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Search: id:A128018
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| A128018 |
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Expansion of (1-4x)/(1-2x+4x^2). |
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+0
7
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| 1, -2, -8, -8, 16, 64, 64, -128, -512, -512, 1024, 4096, 4096, -8192, -32768, -32768, 65536, 262144, 262144, -524288, -2097152, -2097152, 4194304, 16777216, 16777216, -33554432, -134217728, -134217728, 268435456
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Hankel transform of A128014(n+1). Binomial transform of A128019.
Hankel transform of A002426(n+1). - Paul Barry (pbarry(AT)wit.ie), Mar 15 2008
Hankel transform of A007971(n+1). [From Paul Barry (pbarry(AT)wit.ie), Sep 30 2009]
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FORMULA
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a(n)=2^n*(cos(pi*n/3)-sqrt(3)*sin(pi*n)/3)
a(n)=A138340(n)/2^n. [From Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Nov 14 2008]
a(n)=2^(n+1)*cos{-pi*(n+1)/3) [From Richard Choulet (richardchoulet(AT)yahoo.fr), Nov 19 2008]
a(n)=sum{k=0..floor((n+1)/2), C(n+1,2k)*(-3)^k}; a(n)=((1+i*sqrt(3))^(n+1)+(1-i*sqrt(3))^(n+1))/2, i=sqrt(-1). [From Paul Barry (pbarry(AT)wit.ie), Oct 21 2009]
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CROSSREFS
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Sequence in context: A070987 A079458 A138230 this_sequence A104537 A019240 A093907
Adjacent sequences: A128015 A128016 A128017 this_sequence A128019 A128020 A128021
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KEYWORD
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easy,sign
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Feb 11 2007
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