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 A213916 #14 Mar 05 2013 14:09:06
%S A213916 1,1,9,1,6,9,54,1,63,6,47,9,19,54,132,1,36,63,95,6,22,47,117,9,120,19,
%T A213916 20262,54,76,132,20194,1,153,36,94,63,91,95,450,6,20235,22,248,47,81,
%U A213916 117,20163,9,140,120,204,19,59,20262,20426,54,305,76,411,132,178
%N A213916 Sum of all odd numbers in Collatz (3x+1) trajectory of n.
%H A213916 T. D. Noe, <a href="/A213916/b213916.txt">Table of n, a(n) for n = 1..10000</a>
%F A213916 a(n) = A033493(n) - A213909(n).
%e A213916 a(5)=6 since Collatz trajectory of 5 is 5,16,8,4,2,1.
%t A213916 Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; Table[Total[Select[Collatz[n], OddQ]], {n, 100}] (* _T. D. Noe_, Mar 05 2013 *)
%Y A213916 Cf. A033493, A213909.
%K A213916 nonn
%O A213916 1,3
%A A213916 _Jayanta Basu_, Mar 05 2013