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