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.

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

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: A368713 A368039 A160558 * A023581 A023574 A210941

Adjacent sequences: A241016 A241017 A241018 * A241020 A241021 A241022

Keyword

nonn,base

Author

Michel Lagneau, Apr 15 2014

Status

approved