cp's OEIS Frontend

A249399 Start with a(1) = 1 then a(n) = smallest number, not already in the sequence, such that a(n) divides concat(a(n-1),a(n)).

%I A249399 #8 Dec 10 2014 03:59:35
%S A249399 1,2,4,5,10,20,8,16,25,50,40,32,64,80,100,125,200,160,128,250,400,320,
%T A249399 256,500,625,1000,800,640,512,1024,1250,2000,1280,1600,2500,3125,5000,
%U A249399 3200,2048,2560,4000,6250,10000,6400,4096,5120,8000,10240,8192,12500,15625
%N A249399 Start with a(1) = 1 then a(n) = smallest number, not already in the sequence, such that a(n) divides concat(a(n-1),a(n)).
%C A249399 Like A249398, but without the constraint a(n) > a(n-1).
%H A249399 Paolo P. Lava, <a href="/A249399/b249399.txt">Table of n, a(n) for n = 1..100</a>
%e A249399 a(1) = 1;
%e A249399 a(2) = 2 -> 12 /2 = 6;
%e A249399 Now we cannot use 3 as the next term because it does not divide 23.
%e A249399 a(3) = 4 -> 24 / 4 = 6;
%e A249399 a(4) = 5 -> 45 / 5 = 9;
%e A249399 Again, 3, 6, 7, 8 and 9 cannot be used as the next term.
%e A249399 a(5) = 10 -> 510 / 10 = 51;
%e A249399 a(6) = 20 -> 1020 / 20 = 51;
%e A249399 a(7) = 8 -> 208 / 8 = 26; etc.
%p A249399 with(numtheory); P:=proc(q) local a,b,k,n; print(1); a:=1; b:={1};
%p A249399 for k from 1 to q do for n from 1 to q do if nops({n} intersect b)<1
%p A249399 then if type((a*10^(1+ilog10(n))+n)/n,integer)
%p A249399 then a:=n; b:=b union {n}; print(n); break;
%p A249399 fi; fi; od; od; end: P(10^12);
%Y A249399 Cf. A171785, A249398, A250745, A250746, A250747.
%K A249399 nonn,base
%O A249399 1,2
%A A249399 _Paolo P. Lava_, Dec 01 2014