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A166336
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Expansion of (1-4x+7x^2-4x^3+x^4)/(1-7x+17x^2-17x^3+7x^4-x^5)
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1
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1, 3, 11, 39, 131, 421, 1309, 3971, 11823, 34691, 100611, 289033, 823801, 2332419, 6566291, 18394911, 51310979, 142587181, 394905493, 1090444931, 3002921271, 8249479163, 22612505091, 61857842449, 168903452401, 460409998851
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| The diagonal sums of number triangle A166335 are 1,0,3,0,11,0,...
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LINKS
| Guo-Niu Han, Enumeration of Standard Puzzles
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FORMULA
| G.f.: (1-4x+7x^2-4x^3+x^4)/((1-x)(1-3x+x^2)^2);
a(n)=1+2*sum{k=0..n, k*C(n+k,2k)}=1+2*sum{k=0..n, (n-k)*C(2n-k,k)}=1+2*A001870(n).
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CROSSREFS
| Sequence in context: A112674 A064086 A089579 * A002783 A007482 A134760
Adjacent sequences: A166333 A166334 A166335 * A166337 A166338 A166339
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Oct 12 2009
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