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 A138848 #2 Mar 30 2012 18:59:21
%S A138848 1,2,5,10,10,13,16,25,40,42,51,49,65,58,83,94,108,143,141,208,184,294,
%T A138848 241,333,319,486,424,689,559,959,744,1082,990,1251,1319,1470,1478,
%U A138848 1765,2047,2144,2330,2649,2707,2900,2874,3011,3096,3455
%N A138848 Diagonal sums of a Collatz triangle.
%C A138848 Diagonal sums of A138895.
%F A138848 a(n)=sum{k=0..floor(n/2), A092892(n-2k)}
%K A138848 easy,nonn
%O A138848 0,2
%A A138848 _Paul Barry_, Mar 31 2008, Apr 02 2008