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A210766
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Number of 8-hoops with n symbols and no a-rooted trees.
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4
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1, 13, 141, 1204, 7570, 36021, 136948, 436696, 1212399, 3013165, 6843991, 14431308, 28591576, 53726869, 96473910, 166535536, 277726093, 449264781, 707353489, 1087078180
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listen;
history;
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internal format)
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: x*(1+x)*(1+3*x+57*x^2+262*x^3+582*x^4+321*x^5+34*x^6)/(1-x)^9. [Colin Barker, Apr 17 2012]
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MAPLE
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(n^8-8*n^7+36*n^6-92*n^5+155*n^4-148*n^3 +88*n^2-16*n)/16 ;
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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