/usr/share/maxima/5.35.1/demo/sumcon.dem is in maxima-sage 5.35.1-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | 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]);
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