Serial number with Prefix or Suffix

<?php
$dictionary['Opportunity']['fields']['opportunity_index'] =
    array (
      'name' => 'opportunity_index',
      'vname' => 'LBL_OPP_INDEX',
      'type' => 'int',
      'readonly' => true,
      'len' => 11,
      'required' => true,
      'auto_increment' => true,
      'unified_search' => true,
      'full_text_search' => 
      array (
        'boost' => 3,
      ),
      'comment' => 'Visual unique identifier',
      'duplicate_merge' => 'disabled',
      'disable_num_format' => true,
      'studio' => 
      array (
        'quickcreate' => false,
      ),
    );
	
$dictionary['Opportunity']['indices']['number'] =	
    array (
      'name' => 'oppnumk',
      'type' => 'unique',
      'fields' => 
      array (
        0 => 'opportunity_index',
      ),
    );

$dictionary['Opportunity']['indices'][1] =	
    array (
      'name' => 'opportunity_index',
      'type' => 'unique',
      'fields' => 
      array (
        0 => 'opportunity_index',
      ),
    );
?>

<?php

class my_OpportunitiesHookImpl
{
    public function afterSave($bean, $event, $arguments)
    {
		$prefix = "OPP#";
		$suffix = "_crm";
		//Prevent endless loop by checking alread set number:
        if ($bean->opportunity_number_c == "") { 
            $number = $bean->opportunity_index;
            $number = "000000" . $number;
            $number = substr($number, -6);
            $opp = BeanFactory::getBean('Opportunities', $bean->id);
            $opp->opportunity_number_c = $prefix;
            $opp->opportunity_number_c .= $number;
            $opp->opportunity_number_c .= $suffix;
            $opp->save();
        }
	}

}