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Search: id:A106247
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| A106247 |
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Expansion of (1+2x-x^2-2x^3+x^4)/(1-x^2)^3. |
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+0
2
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| 1, 2, 2, 4, 4, 6, 7, 8, 11, 10, 16, 12, 22, 14, 29, 16, 37, 18, 46, 20, 56, 22, 67, 24, 79, 26, 92, 28, 106, 30, 121, 32, 137, 34, 154, 36, 172, 38, 191, 40, 211, 42, 232, 44, 254, 46, 277, 48, 301, 50, 326, 52, 352, 54, 379, 56, 407, 58, 436, 60, 466, 62, 497, 64, 529, 66
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OFFSET
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0,2
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COMMENT
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Diagonal sums of number triangle A106246. Transform of C(2,n)=(1,2,1,0,0,0,...) under the mapping that takes g(x) to (1/(1-x^2))g(x/(1-x^2)).
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FORMULA
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a(n)=sum{k=0..floor(n/2), C(n-k, k)C(2, n-2k)}; a(2n)=A000124(n); a(2n+1)=A005843(n+1).
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CROSSREFS
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Sequence in context: A008645 A018819 A127370 this_sequence A094909 A029008 A136343
Adjacent sequences: A106244 A106245 A106246 this_sequence A106248 A106249 A106250
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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), Apr 26 2005
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