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A241019 Let x(1)x(2)... x(n) denote the decimal expansion of a number p having an index j such that x(j) = 1 and x(i) = 3 for i <> j.  The sequence lists the smallest index j such that p is prime, or 0 if no such prime exists. 5
1, 2, 3, 2, 2, 4, 2, 6, 5, 5, 5, 0, 3, 8, 1, 11, 7, 6, 4, 5, 11, 5, 0, 0, 9, 11, 0, 5, 5, 0, 4, 5, 17, 19, 19, 6, 0, 3, 9, 35, 1, 27, 24, 32, 0, 36, 14, 11, 34, 14, 22, 0, 17, 53, 0, 47, 11, 0, 16, 3, 0, 15, 0, 39, 22, 40, 27, 39, 0, 19, 2, 19, 48, 2, 43, 19 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Except 0, the corresponding primes are 13, 313, 3313, 31333, 313333, 3331333, 31333333, 333331333, 3333133333, 33331333333, 333313333333, 0, 33133333333333, ... .

LINKS

Table of n, a(n) for n=1..76.

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]:=3:

     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, `, j):

         else

         T[j]:=3:

         fi:

         od:

          if ii=0

           then

           printf(`%d, `, 0):

           else

          fi:

       od:

CROSSREFS

Cf. A241018, A241020.

Sequence in context: A295312 A212174 A160558 * A023581 A023574 A210941

Adjacent sequences:  A241016 A241017 A241018 * A241020 A241021 A241022

KEYWORD

nonn,base

AUTHOR

Michel Lagneau, Apr 15 2014

STATUS

approved

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Last modified August 8 02:45 EDT 2020. Contains 336290 sequences. (Running on oeis4.)