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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
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
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
KEYWORD
nonn,base
AUTHOR
Michel Lagneau, Apr 15 2014
STATUS
approved