The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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
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
KEYWORD
nonn,base
AUTHOR
Vincenzo Librandi, Jul 03 2009
STATUS
approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

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