%I A018238
%S A018238 1,21,3121,41213121,5121312141213121,
%T A018238 61213121412131215121312141213121,
%U A018238 7121312141213121512131214121312161213121412131215121312141213121
%N A018238 Add 1 to leading digit and put in front.
%C A018238 The concatenation of first n terms (if n is small) yields a palindrome: 
               1, 121, 1213121, etc. - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), 
               Apr 08 2003
%C A018238 Comments from M. F. Hasler (www.univ-ag.fr/~mhasler), May 05 2008 (Start): 
               This is not the case from n=10 on: According to the formula in A123121 
               A082215(10) has an even number of digits, the middle digits being 
               "10". (In a strict sense, e.g. Def. 3 of the first reference there, 
               A082215(9) is the last Zimin word on the alphabet {1,...,9}, though.)
%C A018238 While there is less ambiguity about the definition of A018238(10), it 
               is not clear if A018238(11) should start with "11..." or with "10..." 
               (the largest digit of all subsequent terms being "9"). According 
               to the formula in A123121, a(100) has 3 digits more than a(99), so 
               the first choice seems appropriate and has been adopted for the given 
               PARI code.
%C A018238 However, it corresponds to a modified definition, "a(n) = concatenation 
               of n and all preceding terms". a(3) is the only prime term up to 
               a(14) included. The sequence is (1,0,1,0,1,0,...) (mod 3), at least 
               up to a(20). (End)
%H A018238 M. F. Hasler, <a href="b018238.txt">Table of n, a(n) for n=1,...,11</
               a>.
%o A018238 (PARI) A018238(n,t="")=for(k=2,n,t=Str(t,k-1,t));eval(Str(n,t)) - M. 
               F. Hasler (www.univ-ag.fr/~mhasler), May 05 2008
%Y A018238 Cf. A001511.
%Y A018238 Cf. A082215, A123121.
%Y A018238 Sequence in context: A114934 A098375 A095154 this_sequence A098724 A078395 
               A153833
%Y A018238 Adjacent sequences: A018235 A018236 A018237 this_sequence A018239 A018240 
               A018241
%K A018238 nonn,base
%O A018238 1,2
%A A018238 N. J. A. Sloane (njas(AT)research.att.com), Michael Minic (minic(AT)mtsu.edu)