Hi eveyone.
I need to display row number as seperate column with Row number as label in Custom LWC datatable. For every record should display serial number as seperate column with header. 
NOTE: I am not asking about show-row-number= true.
I should display row number as seperate field/column in table.

<c-custom-type-component
                            class="POdataTable slds-table_header-fixed_container slds-scrollable_x slds-border_top" 
                            key-field="Id" 
                            data={POrecords}
                            columns={columns} 
                            selected-rows={preSelectedRows} 
                            onrowaction={getPopUpInfo}
                            onpicklistchanged={tablePicklistChanged} 
                            onchangeofreturnqty={handelReturnQty}   
                            onselectedrow={handelSelectedRow}   
                            hide-checkbox-column                     
                        ></c-custom-type-component>

@track columns = [
{
            label: 'Row Number', cell: (row, index) => index + 1 
        }
]
If I am wrong PLEASE let me know. Thanks.