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 A162423 Primes whose decimal expansion has the form XYYYX, for nonzero numbers X and Y, where Y is a single digit. 7
 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 (list; graph; refs; listen; history; text; internal format)
 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

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Last modified June 18 07:40 EDT 2024. Contains 373469 sequences. (Running on oeis4.)