[seqfan] Numbers impossible to produce

[Eric Angelini]

Hello SeqFans,

The integer 126 produces 38 like this:

 1 2 6
  3 8

A digit on the base line is the addition
of the two closest digits above it.

What does the integer 176 produce?
We decide that if the sum a+b of the said
digits is greater than 9, than we subtract
a from b (or b from a if a > b):

 1 7 6
  8 1

So, we managed to produce 38 and 81; but
what could be the smallest number that
would be impossible to produce, according
to the above rule?

Best,
É.