<?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;
}