A178555 Primes with exactly six 6's.

16666669, 26666663, 26666669, 46666661, 46666663, 56666663, 60666667, 63666661, 64666661, 64666663, 64666669, 66066661, 66166663, 66466661, 66466667, 66466669, 66606667, 66616663, 66626663, 66646667, 66656663

Offset: 1

Author

Lekraj Beedassy, May 29 2010

Keywords

• nonn
• base
• look

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A038618, A178550-A178554, A178556-A178558.

Programs

Maple

f:= proc(m) local R, L, s, k, t,x;
  R:= NULL;
  for k from 9^(m-6) to 2*9^(m-6)-1 do
    t:= Vector(subs([8=9,7=8,6=7],convert(k,base,9)[1..m-6]));
    for s in combinat:-choose([$2..m],m-7) do
      L:= Vector(m,6);
      L[[1,op(s)]]:= t;
    if L[-1] = 0 then next fi;
      x:= add(L[i]*10^(i-1),i=1..m);
      if isprime(x) then R:= R, x fi;
  od od:
  op(sort([R]));
end proc:
f(8); # Robert Israel, May 08 2018