<?php
$number=9;
$result=generateSeries($number);
print_r($result);
function generateSeries($number,$seriesCount=100)
{
    if($number>0 && $number<=9)
    {
        $result=array();
        $result[]=$number;
        for($x=0;$x<$seriesCount;$x++)
        {
            if($x%2!=0)
            {
                $result[]=end($result)+20;
            }
            else
            {
                $result[]=end($result)+10;
            }
        }
    }
    return $result;
}