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 A172393 G.f. satisfies: A(x) = G(x/A(x)^2) and G(x) = A(x*G(x)^2) = Sum_{n>=0} C(2n,n)*C(2n+2,n+1)/(n+2)*x^n is the g.f. of A172392. 2
 1, 4, -2, 8, -20, 96, -324, 1648, -6348, 33200, -137848, 732640, -3193296, 17148608, -77335400, 418289696, -1934677436, 10518803376, -49611450120, 270796872160, -1297234193744, 7102371571840, -34458382484976, 189117499963840 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS FORMULA G.f. satisfies: A(x) = Sum_{n>=0} A000108(n+1)*A000984(n)*x^n/A(x)^(2n), where A000108 is the Catalan numbers and A000984 is the central binomial coefficients. Self-convolution equals A172391. EXAMPLE G.f.: A(x) = 1 + 4*x - 2*x^2 + 8*x^3 - 20*x^4 + 96*x^5 - 324*x^6 +... A(x)^2 = 1 + 8*x + 12*x^2 + 28*x^4 + 264*x^6 + 3720*x^8 +... where A(x)^2 equals the g.f. of A172391: A172391=[1,8,12,0,28,0,264,0,3720,0,63840,0,1232432,0,25731216,0,...]. Let G(x) = A(x*G(x)^2) = Sum_{n>=0} C(2n+2,n+1)/(n+2)*C(2n,n)*x^n: G(x) = 1 + 2*2*x + 5*6*x^2 + 14*20*x^3 + 42*70*x^4 + 132*252*x^5 +... PROG (PARI) {a(n)=local(G=sum(m=0, n, binomial(2*m, m)*binomial(2*m+2, m+1)/(m+2)*x^m)+x*O(x^n)); polcoeff((x/serreverse(x*G^2))^(1/2), n)} CROSSREFS Cf. A172391, A172392. Sequence in context: A130078 A230900 A204449 * A245340 A040174 A084477 Adjacent sequences:  A172390 A172391 A172392 * A172394 A172395 A172396 KEYWORD sign AUTHOR Paul D. Hanna, Feb 05 2010 STATUS approved

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