A228627 - OEIS

%I #13 Oct 06 2017 18:27:19

%S 11311,11411,13313,13513,13613,13913,17117,17317,17417,19219,19319,

%T 19819,19919,21121,21221,21521,21821,23623,27127,27427,27527,27827,

%U 29129,29429,29629,31231,31531,33533,37337,37537,39139,39239,39439,39839,41141,41341,41641

%N Primes of the form abcabc..abcab.

%C The sequence appears to be infinite. The number of terms below 10^1000 is 782.

%H Shyam Sunder Gupta, <a href="/A228627/b228627.txt">Table of n, a(n) for n = 1..500</a>

%e a(2)= 11411 is in the sequence because it is a prime of the form abcab.

%t s[n_]:=Select[Union@Flatten@Table[FromDigits@Flatten@Join[IntegerDigits@Table[b, {n}], {IntegerDigits@Floor[b/10]}], {b, 100, 999}], PrimeQ]; Array[s, 2]//Flatten

%t Select[FromDigits[Join[#,{#[[1]]},{#[[2]]}]]&/@Select[Tuples[Range[0,9],3], #[[1]]> 0&],PrimeQ] (* _Harvey P. Dale_, Oct 06 2017 *)

%K nonn,base

%O 1,1

%A _Shyam Sunder Gupta_, Aug 28 2013