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

1,1

Links

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

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

Crossrefs

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

Sequence in context: A192203 A248204 A365812 * A255164 A330247 A365853

Adjacent sequences: A178552 A178553 A178554 * A178556 A178557 A178558

Keyword

nonn,base,look

Author

Lekraj Beedassy, May 29 2010

Status

approved