A074345 - OEIS

%I #14 Jan 26 2022 18:26:53

%S 9,11,21,33,39,71,73,81,101,123,193,257,271,293,379,387,407,627,669,

%T 931,1073,1179,1273,1481,2587,2627,2923,3063,3617,3931,4073,4093,4199,

%U 4491,4801,5387,5647,5739,5859,5979,6149,6369,7527,8053,8207,8647,8949,8981

%N a(1) = 9; a(n) is smallest number > a(n-1) such that the juxtaposition a(1)a(2)...a(n) is a prime.

%H Harvey P. Dale, <a href="/A074345/b074345.txt">Table of n, a(n) for n = 1..200</a>

%t a[1] = 9; a[n_] := a[n] = Block[{k = a[n - 1] + 1 + Mod[a[n - 1], 2], c = IntegerDigits @ Table[ a[i], {i, n - 1}]}, While[ !PrimeQ[ FromDigits @ Flatten @ Append[c, IntegerDigits[k]]], k += 2]; k]; Table[ a[n], {n, 48}] (* _Robert G. Wilson v_ *)

%t nxt[{j_,a_}]:=Module[{c=a+2},While[CompositeQ[j*10^IntegerLength[c]+c],c+=2];{j*10^IntegerLength[c]+c,c}]; NestList[nxt,{9,9},50][[All,2]] (* _Harvey P. Dale_, Jan 26 2022 *)

%Y Cf. A046259, A069611, A074336, A074338, A074339, A074340, A074341, A074342, A074343, A074344, A074346.

%K nonn,base

%O 1,1

%A _Zak Seidov_, Sep 23 2002

%E Corrected and extended by _Robert G. Wilson v_, Aug 05 2005