How to check if SalesInvoice is printed and get the Invoice No.

Hello.  Is there a way using the SDK/API in .NET, to determine if a SalesInvoice has been printed and assigned an Invoice No.?  And where in the API can I find the Invoice No.?

These seem like common questions, so I feel sure I must be overlooking something obvious.  But I cannot find either piece of information on the SalesInvoice object.

Thank you.