This is one of the files posted at the web site
http://www.math.usf.edu/~saito/DNAweb/.
In this page, Mathematica programs and their outputs
obtained by Jonathan Burns are posted.
Tables contain lists of ``prime'' assembly words.
An assembly graph is ``prime'' (defined by J. Burns)
if it does not contain a proper sub-word that is an assembly word.
A prime assembly word is irreducible,
while 1221 is irreducible but not prime.
An assembly word is ``palindromic'' if it is equivalent to
its reverse.