gensumindex:0$
y:sum(a[i]*x^i,i,0,inf);
y1:diff(y,x);
y2:diff(y1,x);
(x^2+1)*y2+3*x*y1+2*y;
expand(%);
factor(%);
intosum(%)$
bashindices(%);
changevar(%,(j4-2)-j,j,j4);
niceindices(%);
sumcontract(%);
factor(%);
part(%,1);
%/x^i=0;
solve(%,a[i+2]);