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A043452 Numbers having four 7's in base 8.

%I A043452 #15 Apr 24 2021 20:51:01
%S A043452 4095,8191,12287,16383,20479,24575,28671,29183,29695,30207,30719,
%T A043452 31231,31743,32255,32319,32383,32447,32511,32575,32639,32703,32711,
%U A043452 32719,32727,32735,32743,32751,32759,32760,32761,32762,32763,32764,32765,32766,36863,40959,45055
%N A043452 Numbers having four 7's in base 8.
%H A043452 Robert Israel, <a href="/A043452/b043452.txt">Table of n, a(n) for n = 1..10000</a>
%p A043452 G:= proc(x,c,d) local L,m1,m2;
%p A043452      L:= convert(x,base,7);
%p A043452      m2:= nops(c);
%p A043452      m1:= min(nops(L),m2);
%p A043452      8^d-1 + add((L[i]-7)*8^(c[i]-1),i=1..m1) - 7*add(8^(c[i]-1),i = m1+1..m2)
%p A043452 end proc:
%p A043452 sort([seq(seq(G(x,c,6), x = 0 .. 7^2-1), c=combinat:-choose(6,2))]); # _Robert Israel_, Sep 24 2017
%t A043452 Select[Range[0, 10^5], DigitCount[#, 8, 7]==4 &] (* _Vincenzo Librandi_, Sep 25 2017 *)
%o A043452 (PARI) isok(n) = #select(x->(x==7), digits(n, 8)) == 4; \\ _Michel Marcus_, Sep 25 2017
%Y A043452 Cf. A007094.
%K A043452 nonn,base
%O A043452 1,1
%A A043452 _Clark Kimberling_