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 A055947 #15 May 14 2022 17:12:22
%S A055947 0,0,0,2,0,-2,4,2,0,8,0,-8,8,0,-8,8,0,-8,16,8,0,16,8,0,16,8,0,26,0,
%T A055947 -26,20,-6,-32,14,-12,-38,32,6,-20,26,0,-26,20,-6,-32,38,12,-14,32,6,
%U A055947 -20,26,0,-26,52,26,0,46,20,-6,40,14,-12,58,32,6,52,26,0,46,20,-6,64,38,12,58,32,6,52,26,0,80,0,-80,56,-24,-104,32,-48
%N A055947 n - reversal of base 3 digits of n (written in base 10).
%C A055947 a(n) is even.
%H A055947 Indranil Ghosh, <a href="/A055947/b055947.txt">Table of n, a(n) for n = 0..20000</a>
%F A055947 a(n) = n - A030102(n).
%e A055947 For n = 5, the reversal of base 3 digits of n (written in base 10) is 7. So, a(5) = 5 - 7 = -2. - _Indranil Ghosh_, Feb 01 2017
%t A055947 Table[n-FromDigits[Reverse[IntegerDigits[n,3]],3],{n,0,90}] (* _Harvey P. Dale_, May 14 2022 *)
%o A055947 (PARI) a(n) = n - fromdigits(Vecrev(digits(n, 3)), 3); \\ _Michel Marcus_, Aug 09 2019
%Y A055947 Cf. A030102, A056965.
%K A055947 base,sign
%O A055947 0,4
%A A055947 _Henry Bottomley_, Jul 18 2000