#awk - 27
{while(i<$0)printf"%c",i++}
To give the parameter on stdin run it like:
awk '{while(i<$0)printf"%c",i++}' <<<96
Just for fun: The "think positive version" starting with a definitive yes:
yes|head -96|awk '{printf"%c",NR-1}'
NR-1 is needed to print (char)0 for NR==1. :-(
And why don't we have a no command? That's kinda mean!