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 A038557 #7 Mar 04 2020 22:50:11
%S A038557 0,2,1,4,8,0,8,0,4,10,14,15,22,26,18,7,2,3,20,21,25,5,6,1,17,9,13,28,
%T A038557 32,33,40,44,36,52,47,48,64,68,69,76,80,72,61,56,57,19,23,24,4,8,0,16,
%U A038557 11,12,56,57,61,68,69,64,80,72,76,11,12,16,23,24,19,8,0,4,47,48,52,32
%N A038557 Periodic derivative of n in base 3.
%D A038557 Simmons, G. J. The structure of the differentiation digraphs of binary sequences. Ars Combin. 35 (1993), A, 71-88. Math. Rev. 95f:05052.
%F A038557 If n=b_k b_{k-1} ... b_0 in base 3, a(n) is number with ternary expansion (b_k+b_{k-1}) (b_{k-1}+b_{k-2}) ... (b_1+b_0) (b_0+b_{k}).
%e A038557 14=112->200 so a(14)=18.
%Y A038557 Cf. A038554-A038556.
%K A038557 nonn,nice,easy
%O A038557 0,2
%A A038557 _N. J. A. Sloane_
%E A038557 Corrected and extended by _Naohiro Nomoto_, Apr 08 2001