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.

17, 0, 1777, 71777, 0, 0, 77777177, 0, 1777777777, 71777777777, 0, 7177777777777, 17777777777777, 0, 7717777777777777, 0, 0, 7777177777777777777, 71777777777777777777, 0, 7777717777777777777777, 77717777777777777777777, 0, 7777771777777777777777777

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: A185685 A144692 A335264 * A176728 A300909 A088469

Adjacent sequences: A241024 A241025 A241026 * A241028 A241029 A241030

Keyword

nonn,base

Author

Michel Lagneau, Apr 15 2014

Status

approved