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A116413
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Expansion of (1+x)/(1-2x-x^2-x^3).
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3
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1, 3, 7, 18, 46, 117, 298, 759, 1933, 4923, 12538, 31932, 81325, 207120, 527497, 1343439, 3421495, 8713926, 22192786, 56520993, 143948698, 366611175, 933692041, 2377943955, 6056191126, 15424018248, 39282171577, 100044552528, 254795294881, 648917313867
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Diagonal sums of number triangle A116412. A078058 is an alternating sign version.
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FORMULA
| a(n)=2a(n-1)+a(n-2)+a(n-3); a(n)=sum{k=0..floor(n/2), sum{j=0..n-k, C(k+1,j)C(n-k-j,k)2^(n-2k-j)}}.
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MATHEMATICA
| CoefficientList[Series[(1+x)/(1-2x-x^2-x^3), {x, 0, 50}], x] (* or *) LinearRecurrence[{2, 1, 1}, {1, 3, 7}, 50] (* From Vladimir Joseph Stephan Orlovsky, Jan 31 2012 *)
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CROSSREFS
| Sequence in context: A191826 A114713 A078058 * A052960 A059512 A094297
Adjacent sequences: A116410 A116411 A116412 * A116414 A116415 A116416
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KEYWORD
| easy,nonn,changed
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Feb 13 2006
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