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A128213
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Expansion of (1-x+2x^2-2x^3)/(1-x+x^2)^2.
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1
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1, 1, 1, -1, -4, -4, 1, 7, 7, -1, -10, -10, 1, 13, 13, -1, -16, -16, 1, 19, 19, -1, -22, -22, 1, 25, 25, -1, -28, -28, 1, 31, 31, -1, -34, -34, 1, 37, 37, -1, -40, -40, 1, 43, 43, -1, -46, -46, 1, 49, 49
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,5
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COMMENTS
| a(n+1) is the Hankel transform of {1,0,1,3,9,28,90,297,1001,3432,11934,...}, cf. A000245. Binomial transform of A128214.
a(n+2) is the Hankel transform of A014138. - Paul Barry (pbarry(AT)wit.ie), Mar 15 2008
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FORMULA
| a(n)=cos(pi*n/3)+(2n/sqrt(3)-1/sqrt(3))*sin(pin/3);
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CROSSREFS
| Sequence in context: A021878 A016495 A047213 * A171716 A016706 A138679
Adjacent sequences: A128210 A128211 A128212 * A128214 A128215 A128216
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KEYWORD
| easy,sign
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Feb 19 2007
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