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 A157143 A transform of the Motzkin numbers. 2
 1, -1, -1, 0, 2, 1, -1, -4, -2, 5, 11, 0, -21, -24, 18, 68, 42, -100, -203, -17, 428, 521, -340, -1544, -1019, 2252, 4892, 606, -10297, -13331, 7821, 39310, 28028, -56893, -130394, -22239, 272991, 370641, -193874, -1081694, -821669, 1536026, 3707766, 798376 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Hankel transform is A157144. LINKS FORMULA G.f.: (1-x)/(1+x^2+x^3)*c((x/(1+x^2+x^3))^2), c(x) the g.f. of A000108. - (The formula does not match the entries, even if A000108 is replaced by A001006. R. J. Mathar, Feb 06 2015) a(n)=sum{k=0..n, (-1)^C(n-k+1,2)*C(floor((n-k)/2),k)*A001006(k)}. PROG (PARI) A157143(n)=vector(n++, k, (-1)^binomial(n+1-k, 2)*binomial((n-k)\2, k-1))*Vec(serreverse(x/(1+x+x^2+O(x^n))))~ \\ M. F. Hasler, Feb 09 2015 CROSSREFS Cf. A001006. Sequence in context: A123199 A212282 A157125 * A112096 A217874 A229118 Adjacent sequences:  A157140 A157141 A157142 * A157144 A157145 A157146 KEYWORD easy,sign AUTHOR Paul Barry, Feb 24 2009 STATUS approved

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