A069609 - OEIS

%I #15 May 06 2022 12:51:30

%S 7,1,9,3,3,3,17,7,11,37,11,9,31,9,17,13,93,3,167,67,119,93,31,33,143,

%T 99,297,91,69,83,1,33,23,27,199,333,123,549,17,67,141,33,39,167,21,

%U 217,279,419,69,517,71,451,171,39,191,93,43,11,303,777,33,67,207,369,489

%N a(1) = 7; a(n) = smallest number such that the juxtaposition a(1)a(2)...a(n) is a prime.

%H Harvey P. Dale, <a href="/A069609/b069609.txt">Table of n, a(n) for n = 1..200</a>

%e a(7) = 17 and the number 71933317 is a prime.

%t a[1] = 7; a[n_] := a[n] = Block[{k = 1, c = IntegerDigits @ Table[ a[i], {i, n - 1}]}, While[ !PrimeQ[ FromDigits @ Flatten @ Append[c, IntegerDigits[k]]], k += 2]; k]; Table[ a[n], {n, 67}] (* _Robert G. Wilson v_, Aug 05 2005 *)

%t nxt[{j_,a_}]:=Module[{k=1},While[CompositeQ[j*10^IntegerLength[k]+k],k++];{j*10^IntegerLength[k]+k,k}]; NestList[nxt,{7,7},70][[All,2]] (* _Harvey P. Dale_, May 06 2022 *)

%Y Cf. A069602, A069604, A046257, A074343, A092528, A069603, A069605, A069606, A069607, A069608, A069609, A069610, A069611, A111525.

%K nonn,base

%O 1,1

%A _Amarnath Murthy_, Mar 26 2002

%E More terms from _Jason Earls_, Jun 13 2002