A162423 Primes whose decimal expansion has the form XYYYX, for nonzero numbers X and Y, where Y is a single digit.

13331, 15551, 16661, 19991, 72227, 75557, 76667, 78887, 79997, 1177711, 1333313, 1355513, 1377713, 1399913, 1711117, 1755517, 1766617, 1777717, 1966619, 1977719, 2311123, 2333323, 2922229, 2944429, 2955529, 2977729, 3111131

Offset

1,1

Comments

There can be no prime whose middle three digits are "000" because it would equal X*(10^Floor[Log[10,X]+1] + 1). - Robert G. Wilson v, Jul 11 2009

Links

Robert G. Wilson v, Table of n, a(n) for n = 1..10895

Mathematica

f[n_] := Block[{len = Floor[ Log[10, n] + 1]}, Select[10^(3 + len) n + 10^len*Table[k (10^3 - 1)/9, {k, 9}] + n, PrimeQ@# &]]; Array[f, 31] // Flatten (* Robert G. Wilson v, Jul 11 2009 *)
Select[FromDigits/@Flatten[Table[Join[IntegerDigits[x], PadRight[{}, 3, y], IntegerDigits[ x]], {x, 40}, {y, Range[9]}], 1], PrimeQ] (* Harvey P. Dale, Jun 28 2020 *)

Prog

(Magma) m:=3; [p: d in [1..9], n in [1..40 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)]; // Vincenzo Librandi, Sep 14 2013

Crossrefs

Sequence in context: A034625 A283155 A254851 * A176465 A185503 A333014

Adjacent sequences: A162420 A162421 A162422 * A162424 A162425 A162426

Keyword

nonn,base

Author

Vincenzo Librandi, Jul 03 2009

Status

approved