Creating a pdf page and want to display row number in first column

Creating a pdf page and want to display row number in first column. I found solution to use apex:variable and increment it.

<apex:variable value="{!0}" var="index"/>
<apex:pageBlockTable value="{!salesOrderItems}" var="salesOrderItem" border="1px">
<apex:variable var="index" value="{!index + 1}"/>
<apex:column>
<apex:facet name="header">
<apex:outputLabel value="Number" />
</apex:facet>
<apex:outputLabel value="{!index}" />
</apex:column>
</apex:pageBlockTable>

But in every row '0' is displaying