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A154949
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Diagonal sums of Riordan array A154948.
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1
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1, 1, 3, 5, 10, 18, 34, 62, 115, 211, 389, 715, 1316, 2420, 4452, 8188, 15061, 27701, 50951, 93713, 172366, 317030, 583110, 1072506, 1972647, 3628263, 6673417, 12274327, 22576008, 41523752, 76374088, 140473848, 258371689, 475219625
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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FORMULA
| G.f.: 1/((1-x^2)(1-x-x^2-x^3));
a(n)=sum{k=0..floor(n/2), sum{j=0..n-k+1, C(n-k+1-j,k+1)C(k-1,j)}}.
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MATHEMATICA
| a=0; b=0; c=0; lst={}; Do[z=a+b+c+1; AppendTo[lst, z]; a=b; b=c; c=z; z=a+b+c; AppendTo[lst, z]; a=b; b=c; c=z, {n, 5!}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Feb 17 2010]
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CROSSREFS
| Sequence in context: A054179 A010049 A094986 * A107232 A134522 A001445
Adjacent sequences: A154946 A154947 A154948 * A154950 A154951 A154952
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Jan 17 2009
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