So I've got a request. I'm working on a number set based on a popular numerical sequence. Every value is directly dependent on the values preceding it. If done by hand there is no way to tell a mistake has been made unless I meticulously scour the work for a single flawed cell and then have to erase everything below and to the right of it. I do not like having to do this, so I want to create a spreadsheet function that will do this for me, so I can figure out whether or not this number matrix is finite without tearing any more hair out.

I need a SUMPRODUCT function that will simplify any answer down to one of three variables based upon a ten digit number system. IE: 4 x 4 = 16; 6 + 1 = 7; 7's value is 2 (further explanation upon request). How do I get an input value of 4 in cell B2 and an input value of 4 in C1 to equal an output value of 2 in cell C2? How do I achieve this in a manner where the value in C2 may be incorporated in cells C3 and D2? And so on...

I'd like to be able to do this relatively infinitely in order to discern patterns in a particular number set that would take a few weeks done by hand, full-time.