A228376 - OEIS

%I #24 Sep 08 2022 08:46:05

%S 1711111117,1766666617,2388888823,2399999923,2911111129,2933333329,

%T 2955555529,2966666629,2999999929,3188888831,4111111141,4133333341,

%U 4144444441,4188888841,4322222243,4333333343,4377777743,4388888843,4399999943,4744444447,4766666647

%N Primes of the form XYYYYYYX, where Y is a single digit.

%H Vincenzo Librandi, <a href="/A228376/b228376.txt">Table of n, a(n) for n = 1..1000</a>

%t f[n_]: = Block[{len = Floor[Log[10, n] + 1]}, Select[10^(6 + len) n + 10^len Table[k (10^6 - 1) / 9, {k, 9}] + n, PrimeQ@#&]]; Array[f, 100] // Flatten

%t Select[With[{y=Table[PadRight[{},6,n],{n,9}]},FromDigits/@(Flatten[ Table[ Join[IntegerDigits[k],#,IntegerDigits[k]],{k,1,51,2}]&/@y,1])],PrimeQ]// Sort (* _Harvey P. Dale_, Mar 01 2019 *)

%o (Magma) m:=6; [p: d in [1..9], n in [1..70 by 2] | IsPrime(p) where p is n*(10^(m+t)+1)+d*10^t*(10^m-1) div 9 where t is #Intseq(n)]; //

%Y Cf. A154270, A214290, A162423, A214702, A214291.

%K nonn,base

%O 1,1

%A _Vincenzo Librandi_, Sep 12 2013