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Numbers whose base-3 representation contains no 0's and exactly four 2's.
1

%I #18 Aug 03 2023 17:28:14

%S 80,161,215,233,239,241,404,458,476,482,484,620,638,644,646,692,698,

%T 700,716,718,724,1133,1187,1205,1211,1213,1349,1367,1373,1375,1421,

%U 1427,1429,1445,1447,1453,1835,1853,1859,1861,1907

%N Numbers whose base-3 representation contains no 0's and exactly four 2's.

%C a(A000389(k)) = (161*3^(k-5)-1)/2 for k >= 5. - _Robert Israel_, Sep 21 2020

%H Robert Israel, <a href="/A044993/b044993.txt">Table of n, a(n) for n = 1..10000</a>

%p f:= proc(d) local C, c;

%p C:= combinat:-choose(d,4);

%p c:=(3^(d)-1)/2;

%p op(sort([seq(c+add(3^(i-1),i=t),t=C)]))

%p end proc:

%p seq(f(d),d=4..8); # _Robert Israel_, Sep 21 2020

%t A044993list[upto_]:=Select[Range[upto],DigitCount[#,3,0]==0&&DigitCount[#,3,2]==4&];A044993list[3000] (* _Paolo Xausa_, Aug 03 2023 *)

%Y Cf. A000389, A007089.

%K nonn,base

%O 1,1

%A _Clark Kimberling_