A046258 - OEIS

%I #16 Apr 10 2024 15:27:10

%S 8,9,23,51,69,81,93,129,169,179,181,273,321,321,449,639,769,857,1047,

%T 1213,1233,1443,1587,1637,1953,2433,2599,2639,2901,3261,3681,4059,

%U 5109,5169,5407,5691,6149,6531,7939,8081,8211,8439,8589,8623,8663,8757,9459

%N a(1) = 8; a(n) is smallest number >= a(n-1) such that the juxtaposition a(1)a(2)...a(n) is a prime.

%H Robert Israel, <a href="/A046258/b046258.txt">Table of n, a(n) for n = 1..400</a>

%p A[1]:= 8: A[2]:= 9: x:= 89:

%p for n from 3 to 100 do

%p   for y from A[n-1] by 2 do

%p     z:= x*10^(1+ilog10(y))+y;

%p     if isprime(z) then break fi;

%p   od:

%p   A[n]:= y;

%p   x:= z;

%p od:

%p seq(A[i],i=1..100); # _Robert Israel_, May 30 2018

%t a[1] = 8; a[n_] := a[n] = Block[{k = a[n - 1], c = IntegerDigits @ Table[ a[i], {i, n - 1}]}, While[ !PrimeQ[ FromDigits @ Flatten @ Append[c, IntegerDigits[k]]], k ++ ]; k]; Table[ a[n], {n, 47}] (* _Robert G. Wilson v_, Aug 05 2005 *)

%t nxt[{jp_,a_}]:=Module[{k=a},While[CompositeQ[jp 10^IntegerLength[k]+k],k++];{jp 10^IntegerLength[k]+ k,k}]; NestList[nxt,{8,8},50][[;;,2]] (* _Harvey P. Dale_, Apr 10 2024 *)

%Y Cf. A069610, A074344, A033680, A033679, A033681, A046254, A046255, A046256, A046257, A046259, A111524.

%K nonn,base

%O 1,1

%A _Patrick De Geest_, May 15 1998