cp's OEIS Frontend

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.

%I A241027 #5 Apr 16 2014 17:25:52
%S A241027 17,0,1777,71777,0,0,77777177,0,1777777777,71777777777,0,
%T A241027 7177777777777,17777777777777,0,7717777777777777,0,0,
%U A241027 7777177777777777777,71777777777777777777,0,7777717777777777777777,77717777777777777777777,0,7777771777777777777777777
%N 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.
%C A241027 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).
%H A241027 Michel Lagneau, <a href="/A241027/b241027.txt">Table of n, a(n) for n = 2..150</a>
%p A241027 with(numtheory):nn:=80:T:=array(1..nn):
%p A241027    for n from 2 to nn do:
%p A241027      for i from 1 to n do:
%p A241027      T[i]:=7:
%p A241027      od:
%p A241027        ii:=0:
%p A241027        for j from 1 to n while(ii=0)do:
%p A241027        T[j]:=1:s:=sum('T[i]*10^(n-i)', 'i'=1..n):
%p A241027          if type(s,prime)=true
%p A241027          then
%p A241027          ii:=1: printf(`%d, `,s):
%p A241027          else
%p A241027          T[j]:=7:
%p A241027          fi:
%p A241027        od:
%p A241027           if ii=0
%p A241027            then
%p A241027            printf(`%d, `,0):
%p A241027            else
%p A241027           fi:
%p A241027      od:
%Y A241027 Cf. A241018, A241019, A241020, A241022.
%K A241027 nonn,base
%O A241027 2,1
%A A241027 _Michel Lagneau_, Apr 15 2014