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 A143561 G.f. satisfies: A(x) = ( 1 + x*A(x)/A(-x) )^2. 0
 1, 2, 9, 24, 88, 280, 1064, 3672, 14456, 52184, 210504, 782232, 3210904, 12176792, 50638440, 194956248, 818961080, 3189915224, 13508052104, 53105011480, 226355549400, 896636646936, 3842662060200, 15317408281944, 65946510374136 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Table of n, a(n) for n=0..24. FORMULA G.f. satisfies: (1+x^2)^2 - 2*(1+x^2)*G(x) + (1+x)*G(x)^2 - x*G(x)^3 = 0 where G(x)^2 = A(x) and G(x) = 1 + x*A(x)/A(-x) is the g.f. of A143555. EXAMPLE G.f.: A(x) = 1 + 2*x + 9*x^2 + 24*x^3 + 88*x^4 + 280*x^5 + 1064*x^6 +... A(x)/A(-x) = 1 + 4*x + 8*x^2 + 28*x^3 + 80*x^4 + 308*x^5 + 984*x^6 +... PROG (PARI) {a(n)=local(A=1+x*O(x^n)); for(i=0, n, B=A/subst(A, x, -x); A=(1+x*B)^2); polcoeff(A, n)} CROSSREFS Cf. A143555. Sequence in context: A222667 A122006 A200086 * A363660 A027302 A213720 Adjacent sequences: A143558 A143559 A143560 * A143562 A143563 A143564 KEYWORD nonn AUTHOR Paul D. Hanna, Aug 24 2008 STATUS approved

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Last modified July 15 19:27 EDT 2024. Contains 374334 sequences. (Running on oeis4.)