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A129148
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Expansion of (1-x-sqrt(1-6x-7x^2))/(2(1+2x)).
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0
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1, 2, 8, 36, 180, 956, 5300, 30316, 177604, 1060284, 6427092, 39452364, 244748196, 1532044572, 9664688436, 61380865452, 392148430212, 2518518772604, 16250624534420, 105297028489612, 684865176181348
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Series reversion of x(1-x)/(1+x+2x^2). Hankel transform is 4^C(n+1,2)=A053763(n+1).
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FORMULA
| a(n)=sum{k=0..n, sum{j=0..n, C(n,j)C(n-k,j+k-n)*C(n-k)*3^(j+k-n)}}, C(n)=A000108(n); a(n)=(1/(2*pi))*int(x^n*sqrt(7+6x-x^2)/(2+x),x,-1,7);
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CROSSREFS
| Sequence in context: A166229 A109318 A113327 * A081958 A001540 A129044
Adjacent sequences: A129145 A129146 A129147 * A129149 A129150 A129151
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Apr 01 2007
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