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A280893 a(n) is the maximum prime factor of the concatenation of all the previous terms, with a(1)=1, a(2)=2.

%I A280893 #27 Aug 06 2017 22:08:10
%S A280893 1,2,3,41,43,1063,5479,111031,790000148543,790000148543,
%T A280893 326139075156576200419624217119,326139075156576200419624217119,
%U A280893 326139075156576200419624217119,246787955464079218902570922322710067417716295997334514692275780099917
%N A280893 a(n) is the maximum prime factor of the concatenation of all the previous terms, with a(1)=1, a(2)=2.
%H A280893 Hans Havermann, <a href="/A280893/b280893.txt">Table of n, a(n) for n = 1..15</a>
%e A280893 The maximum prime factor of concat(1,2) = 12 is 3, so a(3) = 3;
%e A280893 The maximum prime factor of concat(1,2,3) = 123 is 41, so a(4) = 41; etc.
%p A280893 with(numtheory): P:= proc(q) local a,b,c,k,n; print(1); print(2); a:=12;for n from 3 to q do b:=ifactors(a)[2]; c:=0; for k from 1 to nops(b) do if b[k][1]>c then c:=b[k][1]; fi; od; a:=a*10^(ilog10(c)+1)+c; print(c); od; end: P(10^2);
%t A280893 a = {1, 2}; Do[AppendTo[a, FactorInteger[FromDigits@ Flatten@ Map[IntegerDigits, a]][[-1, 1]]], {10}]; a (* _Michael De Vlieger_, Jan 10 2017 *)
%Y A280893 Cf. A280894.
%K A280893 nonn,base
%O A280893 1,2
%A A280893 _Paolo P. Lava_, Jan 10 2017
%E A280893 a(12)-a(13) from _Jon E. Schoenfield_, Jan 10 2017
%E A280893 a(14)-a(15) from _Hans Havermann_, Jan 12 2017