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A241027 Smallest prime numbers p of length n having a decimal expansion x(1)x(2)... x(n) such that there exists an index j where x(j) = 1 and x(i) = 7 for i<>j, or 0 if no such prime exists. 2
17, 0, 1777, 71777, 0, 0, 77777177, 0, 1777777777, 71777777777, 0, 7177777777777, 17777777777777, 0, 7717777777777777, 0, 0, 7777177777777777777, 71777777777777777777, 0, 7777717777777777777777, 77717777777777777777777, 0, 7777771777777777777777777 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

The corresponding index of the decimal digit 1 are 1, 0, 1, 2, 0, 0, 6, 0, 1, 2, 0, 2, 1, 0, 3, 0, 0, 5, 2,...(A241020).

LINKS

Michel Lagneau, Table of n, a(n) for n = 2..150

MAPLE

with(numtheory):nn:=80:T:=array(1..nn):

   for n from 2 to nn do:

     for i from 1 to n do:

     T[i]:=7:

     od:

       ii:=0:

       for j from 1 to n while(ii=0)do:

       T[j]:=1:s:=sum('T[i]*10^(n-i)', 'i'=1..n):

         if type(s, prime)=true

         then

         ii:=1: printf(`%d, `, s):

         else

         T[j]:=7:

         fi:

       od:

          if ii=0

           then

           printf(`%d, `, 0):

           else

          fi:

     od:

CROSSREFS

Cf. A241018, A241019, A241020, A241022.

Sequence in context: A198631 A185685 A144692 * A176728 A300909 A088469

Adjacent sequences:  A241024 A241025 A241026 * A241028 A241029 A241030

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Apr 15 2014

STATUS

approved

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Last modified August 14 06:01 EDT 2018. Contains 313748 sequences. (Running on oeis4.)