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G.f. satisfies: A(x) = 1 + x*A(x)^2 / (A(I*x) * A(-I*x)).
5

%I #18 Sep 14 2012 17:14:18

%S 1,1,2,8,26,56,194,832,2866,7904,30690,137000,497706,1491512,6041602,

%T 27557184,102985186,321675648,1333006018,6160815624,23426000186,

%U 75016874488,315357132994,1470462300160,5656904907026,18419315779552,78201118018466,366962271138472

%N G.f. satisfies: A(x) = 1 + x*A(x)^2 / (A(I*x) * A(-I*x)).

%e G.f.: A(x) = 1 + x + 2*x^2 + 8*x^3 + 26*x^4 + 56*x^5 + 194*x^6 + 832*x^7 +...

%e Related expansions begin:

%e A(x)^2 = 1 + 2*x + 5*x^2 + 20*x^3 + 72*x^4 + 196*x^5 + 668*x^6 + 2692*x^7 +...

%e A(I*x)*A(-I*x) = 1 - 3*x^2 + 40*x^4 - 316*x^6 + 4624*x^8 - 50676*x^10 + 811192*x^12 -+...

%o (PARI) {a(n)=local(A=1+x);for(i=1,n,A=1+x*A^2/(subst(A,x,I*x+x*O(x^n))*subst(A,x,-I*x+x*O(x^n))));polcoeff(A,n)}

%o for(n=0,30,print1(a(n),", "))

%Y Cf. A143339, A216681, A216712, A216713.

%K nonn

%O 0,3

%A _Paul D. Hanna_, Jun 13 2012