I have noticed that when I place a test order on my site, the order numbers are not incremental and seem random. Having them incremental would be really helpful as I like to print of the order invoices and file them incrementally
The order depend on the payment(gateway) system you are using. We use the same payment number sent by the system so you can validate the order agains the gateway.
The only order number that will appear in order is the email checkout.