(PARI)
我的(x='x+O('x^N),y0=1,y1=0,N=1);
而(n++,
y1=(1+x*(1+2*t+x*t^2)*y0^2+t*(1-t)*x^2*y0|3+2*x^2*y0*y0');
y1=y1/(1+2*x*t);如果(y1==y0,break());y0=y1;);年;
};
(PARI)
my(s=Ser(concat(1,向量(N+1,N,(2*N)!/(2^n*n!)),g=(1/s-1/s^2)/x);
1-1/subst(g,'x,serreverse(x*g^2*s^2));
};