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A089770 Smallest n-digit prime containing no prime substrings, or 0 if no such number exists. 3
2, 11, 101, 1009, 10009, 100049, 1000081, 10000169, 100000049, 1000000009, 10000000069, 100000000069, 1000000000091, 10000000000099, 100000000000099, 1000000000000091, 10000000000000069, 100000000000000049 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n > 1, a(n) ends in 1 or 9 while other digits can be 0,1,4,6,8 or 9. - Robert Israel, Dec 09 2017

LINKS

Robert Israel, Table of n, a(n) for n = 1..999

EXAMPLE

a(3) = 149 is a term as 1,4,9,14,49 are all nonprimes. 199 is not a member as 19 is a prime.

MAPLE

N:= 1000: # to get terms until the first where a(n) > 10^(n-1)+10*N+9

filter1:= proc(x)

  local k, j;

  for k from 0 to ilog10(x) do

     for j from k to ilog10(x)+1 do

       if isprime(floor((x mod 10^j)/10^k)) then return false fi;

  od od:

  true

end proc:

X:= select(filter1, [seq(seq(10*i+j, j=[1, 9]), i=0..N)]):

filter2:= proc(p, x)

    local k, j;

    if not isprime(p) then return false fi;

    for k from 1 to ilog10(x)+1 do

     if isprime(floor(p /10^k)) then return false fi

    od;

    true;

end proc:

for n from 1 do

found:= false;

for x in X do

    p:= 10^(n-1)+x;

    if filter2(p, x) then A[n]:= p; found:= true; break fi;

od:

if not found then break fi

od:

seq(A[i], i=1..n-1); # Robert Israel, Dec 09 2017

CROSSREFS

Cf. A089768, A033274, A089771.

Sequence in context: A158578 A003617 A114018 * A249447 A199302 A069663

Adjacent sequences:  A089767 A089768 A089769 * A089771 A089772 A089773

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Nov 23 2003

EXTENSIONS

Corrected and extended by David Wasserman, Oct 12 2005

STATUS

approved

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Last modified April 22 14:27 EDT 2019. Contains 322352 sequences. (Running on oeis4.)