$#="%@{[2*length $a]}d";print map"@{[$j+1..($j+=++$i)]}\n",1..$a
$#="%@{[2*length $a]}u";print map"@{[$j+1..($j+=++$i)]}\n",1..$a
$#="%@{[2*length $a]}s";print map"@{[$j+1..($j+=++$i)]}\n",1..$a