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1, 1, 3, 15, 91, 603, 4213, 30537, 227475, 1730787, 13393689, 105089229, 834086421, 6684761125, 54022715451, 439742222071, 3602118427251, 29671013856627, 245613376802185, 2042162142208813, 17047255430494497, 142816973618414817
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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COMMENTS
| The Kn4 triangle sums of A175136 lead to the sequence given above (n>=1). For the definition of the Kn4 and other triangle sums see A180662. [From Johannes W. Meijer, May 6 2011]
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LINKS
| Guo-Niu Han, Enumeration of Standard Puzzles
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MAPLE
| G:=(1+x-sqrt(1-2*x-3*x^2))/(2*x*(1+x)): Gser:=series(G, x=0, 60):1, seq(coeff(Gser, x^(2*n)), n=1..25); (Deutsch)
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CROSSREFS
| Sequence in context: A034954 A077783 A047019 * A171790 A006632 A159928
Adjacent sequences: A099248 A099249 A099250 * A099252 A099253 A099254
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Nov 16 2004
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Nov 18 2004
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