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%I #9 Dec 15 2017 17:41:10
%S 1,2,9,63,594,14058,25627437,5941439657604,150482558208133815048,
%T 2463743660424402357955859435526447,
%U 5941429767504259381561776919813218438160375943419757604,16038354830713282603922637536703240576965473072533033395669335536367159371668297243716038
%N a(1) = 1, a(2) = 2, then the absolute difference of the concatenation of two previous terms and its digit reversal.
%C a(n) is a multiple of 99 for n > 4. Conjecture: The sequence has finitely many nonzero terms. (This would happen when the concatenation of two successive terms becomes a palindrome and the next term is 0.)
%e a(1) = 1, a(2) = 2, a(3) = |12-21| = 9, a(4) = |29-92| = 63, a(5) = |963-369| = 594, a(6) = |63594 - 49536| = 14058, a(7) = |59418018 - 81081495| = 21663477, ...
%t nxt[{a_,b_}]:=Module[{id=Join[IntegerDigits[a],IntegerDigits[b]]},{b,Abs[ FromDigits[ id]- FromDigits[Reverse[id]]]}]; Transpose[NestList[nxt,{1,2},12]][[1]] (* _Harvey P. Dale_, Nov 30 2014 *)
%K base,nonn
%O 1,2
%A _Amarnath Murthy_ and _Jason Earls_, Jul 13 2003
%E Corrected and extended by Mark Hudson (mrmarkhudson(AT)hotmail.com), Jul 23 2004
%E More terms from _David Wasserman_, Feb 11 2005
%E One more term (a(12)) from _Harvey P. Dale_, Nov 30 2014
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