%I #14 May 18 2023 23:49:05

%S 1,2,3,6,5,4,16,8,9,10,14,12,20,26,35,36,37,44,7,40,31,22,19,28,25,32,

%T 39,56,60,70,43,52,49,30,15,48,51,58,59,120,50,64,93,88,65,86,61,168,

%U 101,100,57,68,13,84,155,104,158,54,127,80,133,38,78,144,45,138,18,76

%N Beginning with 1, least positive integer not occurring earlier such that the n-th partial concatenation is a multiple of n.

%H Paul Tek, <a href="/A100769/b100769.txt">Table of n, a(n) for n = 1..10000</a>

%H Paul Tek, <a href="/A100769/a100769.txt">PARI program for this sequence</a>

%e a(7) = 16 as the concatenation 12365416 of first seven terms is a multiple of 7. No number less than 16 and more than 6 fits in.

%t a[1] = 1; a[n_] := a[n] = Block[{t = 1}, While[Mod[FromDigits@ Flatten[IntegerDigits /@ Join[Array[a, n - 1], {t}]], n] != 0 || MemberQ[Array[a, n - 1], t], t++]; t]; Array[a, 68] (* _Giorgos Kalogeropoulos_, May 07 2023 *)

%o (PARI) See Link section.

%Y Cf. A099552, A100770.

%K base,easy,nonn

%O 1,2

%A _Amarnath Murthy_, Nov 27 2004

%E More terms from _Joshua Zucker_, May 27 2005