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Search: id:A104721
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| A104721 |
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Expansion of (1+x)^2/(1-4x^2). |
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+0
3
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| 1, 2, 5, 8, 20, 32, 80, 128, 320, 512, 1280, 2048, 5120, 8192, 20480, 32768, 81920, 131072, 327680, 524288, 1310720, 2097152, 5242880, 8388608, 20971520, 33554432, 83886080, 134217728, 335544320, 536870912, 1342177280, 2147483648
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OFFSET
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0,2
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COMMENT
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Binomial transform is A033113.
Let b(n)=binomial(n-1,(n-1)/2)(1-(-1)^n)/2+binomial(n,n/2)(1+(-1)^n)/2. Then a(n)=sum{k=0..n, b(k)b(n-k)}.
If a(1)=2 is dropped, sequence becomes identical to A084568 (Proof immediate by standard manipulation of the two generating functions.) . - R. J. Mathar (mathar(AT).strw.leidenuniv.nl), May 19 2008
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FORMULA
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a(n)=9*2^n/8+(-2)^n/8-0^n/4
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CROSSREFS
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Adjacent sequences: A104718 A104719 A104720 this_sequence A104722 A104723 A104724
Sequence in context: A076870 A127281 A054774 this_sequence A139407 A107384 A092446
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Mar 20 2005
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