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A178555 Primes with exactly six 6's.

%I A178555 #12 May 08 2018 08:00:43
%S A178555 16666669,26666663,26666669,46666661,46666663,56666663,60666667,
%T A178555 63666661,64666661,64666663,64666669,66066661,66166663,66466661,
%U A178555 66466667,66466669,66606667,66616663,66626663,66646667,66656663
%N A178555 Primes with exactly six 6's.
%H A178555 Robert Israel, <a href="/A178555/b178555.txt">Table of n, a(n) for n = 1..10000</a>
%p A178555 f:= proc(m) local R, L, s, k, t,x;
%p A178555   R:= NULL;
%p A178555   for k from 9^(m-6) to 2*9^(m-6)-1 do
%p A178555     t:= Vector(subs([8=9,7=8,6=7],convert(k,base,9)[1..m-6]));
%p A178555     for s in combinat:-choose([$2..m],m-7) do
%p A178555       L:= Vector(m,6);
%p A178555       L[[1,op(s)]]:= t;
%p A178555     if L[-1] = 0 then next fi;
%p A178555       x:= add(L[i]*10^(i-1),i=1..m);
%p A178555       if isprime(x) then R:= R, x fi;
%p A178555   od od:
%p A178555   op(sort([R]));
%p A178555 end proc:
%p A178555 f(8); # _Robert Israel_, May 08 2018
%Y A178555 Cf. A038618, A178550-A178554, A178556-A178558.
%K A178555 nonn,base,look
%O A178555 1,1
%A A178555 _Lekraj Beedassy_, May 29 2010