  In array-based DNA synthesis, multiple strands of DNA are synthesized in
parallel to reduce the time cost from the sum of their lengths to the length
their shortest common supersequences. To maximize the amount of information
that can be synthesized into DNA within a finite amount of time, we study the
number of unordered sets of $n$ strands of DNA that have a common supersequence
whose length is at most $t$. Our analysis stems from the following connection:
The number of subsequences of A C G T A C G T A C G T ... is the partial sum
(prefix sum) of the fourth-order Fibonacci numbers.
