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Search: id:A059398
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| 1, 2, 6, 17, 51, 154, 473, 1464, 4568, 14332, 45187, 143024, 454217, 1446604, 4618576, 14777451, 47371177, 152110326, 489165277, 1575211177, 5078690936, 16392526502, 52963765321, 171282782902, 554393341371, 1795821017014
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Number of paths in the first quadrant from (0,0) to the line x=n, consisting of steps U=(1,1), D=(1,-1), h=(1,0) and H=(2,0) (in other words, left factors of the paths in A128720). Example: a(2)=6 because we have hh, H, UD, hU, Uh and UU. Row sums of triangle in A132276. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Sep 03 2007
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REFERENCES
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W. Klostermeyer et al., A Pascal rhombus, Fibonacci Quarterly, 35 (1976), 318-328.
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FORMULA
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G.f.: (sqrt((1+x-x^2)/(1-3*x-x^2))-1)/x/2. - Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 20 2004
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MAPLE
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g:=(1/2)*(sqrt((1+x-x^2)/(1-3*x-x^2))-1)/x: gser:=series(g, x=0, 30): seq(coeff(gser, x, n), n=0..25); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Sep 03 2007
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CROSSREFS
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Cf. A128720, A132276.
Sequence in context: A148449 A148450 A153773 this_sequence A157002 A071717 A148451
Adjacent sequences: A059395 A059396 A059397 this_sequence A059399 A059400 A059401
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Jan 29 2001
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EXTENSIONS
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More terms from Larry Reeves (larryr(AT)acm.org), Jan 31 2001
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