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 A204990 #5 Mar 30 2012 18:58:09 %S A204990 1,1,3,2,15,3,7,4,63,15,1023,6,4095,7,15,8,255,63,262143,30,63,1023, %T A204990 2047,12,1048575,4095,262143,14,268435455,15,31,16,1023,255,4095,126, %U A204990 68719476735,262143,4095,60,1048575,63,16383,2046,4095,2047 %N A204990 (1/2)*(A204991). %C A204990 For a guide to related sequences, see A204892. %t A204990 (See the program at A204987.) %Y A204990 Cf. A204987, A204892, A204991. %K A204990 nonn %O A204990 1,3 %A A204990 _Clark Kimberling_, Jan 21 2012