This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A081607 #12 Mar 19 2018 04:18:06
%S A081607 1,1,1,2,2,2,3,3,3,4,5,6,7,7,7,8,8,8,9,10,11,12,12,12,13,13,13,14,15,
%T A081607 16,17,18,19,20,21,22,23,24,25,26,26,26,27,27,27,28,29,30,31,31,31,32,
%U A081607 32,32,33,34,35,36,37,38,39,40,41,42,43,44,45,45,45,46,46,46,47,48,49,50
%N A081607 Number of numbers <= n having at least one 0 in their ternary representation.
%C A081607 a(n) + A081608(n) = n+1.
%H A081607 Robert Israel, <a href="/A081607/b081607.txt">Table of n, a(n) for n = 0..10000</a>
%p A081607 f:= n -> `if`(has(convert(n,base,3),0),1,0):
%p A081607 ListTools:-PartialSums(map(f, [$0..100])); # _Robert Israel_, Mar 18 2018
%t A081607 Accumulate[Boole[Table[DigitCount[n,3,0]>0,{n,0,80}]]] (* _Harvey P. Dale_, Jun 23 2017 *)
%o A081607 (PARI) first(n)=my(s,t); vector(n,k, t=Set(digits(k,3)); s+=(t[1]==0)) \\ _Charles R Greathouse IV_, Sep 02 2015
%Y A081607 Cf. A007089, A077267, A081609, A081610.
%K A081607 nonn
%O A081607 0,4
%A A081607 _Reinhard Zumkeller_, Mar 23 2003