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 A043682 #17 Apr 13 2021 23:06:52 %S A043682 5,9,10,11,13,17,18,19,20,22,23,25,26,27,29,33,34,35,36,38,39,40,44, %T A043682 46,47,49,50,51,52,54,55,57,58,59,61,65,66,67,68,70,71,72,76,78,79,80, %U A043682 88,92,94,95,97,98,99,100,102,103,104,108,110 %N A043682 a(n) = (1/2)*(n-th number whose base-2 representation has exactly 4 runs). %C A043682 Numbers with exactly two runs of 1's in binary. - _Franklin T. Adams-Watters_, Dec 09 2013 %t A043682 Select[Range[250],Length[Split[IntegerDigits[#,2]]]==4&]/2 (* _Harvey P. Dale_, Aug 25 2016 *) %o A043682 (PARI) runs(n)=my(s);while(n, n>>=valuation(if(n%2,n+1,n),2);s++); s %o A043682 is(n)=runs(n>>valuation(n,2))==3 \\ _Charles R Greathouse IV_, Dec 09 2013 %Y A043682 Cf. A023758, A043683, A043684, A043685, A043686. %K A043682 nonn,base %O A043682 1,1 %A A043682 _Clark Kimberling_