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 A210145 #6 Mar 30 2012 17:22:10 %S A210145 2,4,8,14,25,41,74,124,222,390,706,1262,2324,4244,7869,14607,27337, %T A210145 51243,96665,182666,346647,659206,1257287,2402569,4601771,8828741, %U A210145 16969511,32665154,62972932 %N A210145 a(n) = 2^n - A210109(n). %C A210145 This is the number of binary sequences of length n that are not 3-divided. The number that are not 2-divided turned out, surprisingly, to be A000031, so this also seems worth including. %Y A210145 Cf. A210109, A000031, A209970. %K A210145 nonn %O A210145 1,1 %A A210145 _N. J. A. Sloane_, Mar 17 2012