*Decio*

Thank you, looks good to me. I think I may well have misunderstood the initial requirement as 'generate 10 invoice numbers unless a different number is explicitly requested'. I notice that in cell **C3 **you had a relative reference to **B3**; that is simply the invoice number, giving the formula

**= IF( LEN(invoiceNumber)>10, SEQUENCE(1,count,start), invoiceNumber )**

I do not expect to have errors (a #SPILL! error cannot be hidden and, anyway, would need to be corrected) so I removed that test.

I had also played with the complex arithmetic that gives the count of invoices required and obtained a slightly different expression for **count**

= 1 + IMAGINARY( IMPRODUCT( invoiceNumber & "j", "-1-j" ) )

It is possible to read over **IMREAL **without really seeing it but the function **IMAGINARY **jumps out of the page!

*Peter*