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Search: id:A129148
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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
1
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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; listen)
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OFFSET
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0,2
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COMMENT
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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
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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
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Sequence in context: A110837 A109318 A113327 this_sequence A081958 A001540 A129044
Adjacent sequences: A129145 A129146 A129147 this_sequence A129149 A129150 A129151
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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 01 2007
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