Quote:
Originally Posted by Batalov
I did test for the 4th AP term.
 for the lower AP3, 5^2  A(4)
 for the higher AP3, I have not found a trivial factor, but it is composite.
 A_{1} = 5606879602425*2^12900001 prime
 A_{2} = 33*2^29390631 prime
 A_{3} = 33*2^29390645606879602425*2^12900001 prime
 A_{4} = 99*2^29390635606879602425*2^12900011 composite

So, A
_{3} is the top, as I originally guessed and you confirmed. Obviously, I don't know which end is up.
If the common difference is d, the AP3 is A
_{3}  2d, A
_{3}  d, A
_{3}.
I assume A
_{4} was checked for small factors, then subjected to a compositeness test that proved it to be composite, but did not reveal any factors.