Bash + GNU utilities, 96 bytes
u=$[(2**$1+1)/2]
for((;++n<u*4;)){ dc -e "5[p]sp$n^dO$1^<p";}|head -$u|sed -r "s/.*(.).{$1}/\1/"
0-based indexing.
Mitchell Spector
- 8k
- 1
- 17
- 35