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 A055949 #11 Feb 01 2017 16:58:08
%S A055949 0,0,0,0,3,0,-3,-6,6,3,0,-3,9,6,3,0,15,0,-15,-30,15,0,-15,-30,15,0,
%T A055949 -15,-30,15,0,-15,-30,30,15,0,-15,30,15,0,-15,30,15,0,-15,30,15,0,-15,
%U A055949 45,30,15,0,45,30,15,0,45,30,15,0,45,30,15,0,63,0,-63,-126,51,-12,-75,-138,39,-24,-87,-150,27,-36,-99,-162,75,12,-51
%N A055949 n - reversal of base 4 digits of n (written in base 10).
%C A055949 a(n) is a multiple of 3.
%H A055949 Indranil Ghosh, <a href="/A055949/b055949.txt">Table of n, a(n) for n = 0..20000</a>
%F A055949 a(n) = n - A030103(n).
%e A055949 For n = 6, the reversal of base 4 digits of n (written in base 10) is 9. So, a(6) = 6 - 9 = -3. - _Indranil Ghosh_, Feb 01 2017
%t A055949 Table[n-FromDigits[Reverse[IntegerDigits[n,4]],4],{n,0,90}] (* _Harvey P. Dale_, Aug 22 2011 *)
%Y A055949 Cf. A030103, A056965.
%K A055949 base,sign
%O A055949 0,5
%A A055949 _Henry Bottomley_, Jul 18 2000