How to generate each integer number from 1 to (say) n

midweeker

in a random order such that each number (and none outside this range) is returned just once

koogs

create an intlist containing all the required values, call shuffle().

https://processing.org/reference/IntList.html

GoToLoop

final int QTY = 15;
final IntList range = IntList.fromRange(QTY);

println(range);
range.shuffle();
println(range);

exit();