A075598 a(1) = 5 and then the smallest prime that is obtained by placing digits on both sides of the previous term. Or smallest prime that encompasses a(n-1).

5, 151, 11519, 2115193, 121151939, 21211519397, 4212115193971, 342121151939719, 43421211519397199, 2434212115193971993, 224342121151939719937, 122434212115193971993787, 51224342121151939719937871, 2512243421211519397199378719, 325122434212115193971993787197, 93251224342121151939719937871973

Offset: 1

Author

Amarnath Murthy, Sep 28 2002

Keywords

• base
• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..330

Crossrefs

Cf. A075595, A075596, A075597, A075599, A075600, A075601, A075602.

Programs

Maple

f:= proc(n) local m,d,d1,v,x,y,y0,z,found;
  m:= ilog10(n);
  v:= infinity;
  for d from 2 do
    for d1 from 1 to d-1 do
      found:= false;
      for x from 10^(d1-1) to 10^d1-1 while not found do
        if d-d1=1 then y0:= 1 else y0:= 10^(d-d1-1)+1 fi;
        for y from y0 to 10^(d-d1)-1 by 2 do
          z:= y+10^(d-d1)*n + 10^(d-d1+m+1)*x;
          if isprime(z) then v:= min(v,z); found:= true; break fi
      od od;
    od;
    if v < infinity then return v fi
  od
end proc:
A[1]:= 5:
for n from 2 to 20 do
  A[n]:= f(A[n-1])
od:
seq(A[n],n=1..20); # Robert Israel, Aug 28 2018

Extensions

More terms from Sascha Kurz, Jan 20 2003

Terms a(13) and beyond from Robert Israel, Aug 28 2018