I've found how to create an array of the products of variables input into column A and row 1. Thing is, their increase in value is exponential. How do I calculate the sum of each individual integer in the product of two cells (as inputs to a new, as yet used, cell) until I have a value as a single integer?

Example: the value in cell C2 is 16. The value in cell B3 is 16. These two multiplied together, to form a new value in cell C3, become 256. 2+5+6=13. 1+3=4. How do I get an input of 16 twice (again, in cells C2 and B3) to become 4 (in cell C3)?

...Really, that would be, how do I get the inputs of 7 and 7 (that values of the sum of 1+6) to equal 4? (7x7=49, 4+9=13, 1+3=4)

I appreciate whatever help you may offer.

Cheers,
DW.