<?php
$total = 30;
$skip = 5;
 
$res = calc1($total, $skip);
print_r($res);
 
$res = calc2($total, $skip);
print_r($res);
 
 
function calc1($total, $skip) {
	$n = 0;
	$arr = range(1, $total);
 
	while (count($arr) >= $skip) {
		foreach ($arr as $i => $el) {
			$n++;
			if ($n % $skip == 0) unset($arr[$i]);
		}
	}
 
	return $arr;
}
 
function calc2($total, $skip) {
	$n = 0;
	$arr = range(1, $total);
 
	while (count($arr) >= $skip) {
		$n++;
		$val = array_shift($arr);
		if ($n % $skip) $arr[] = $val;
	}
 
	sort($arr);
	return $arr;
}

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