A043682 a(n) = (1/2)*(n-th number whose base-2 representation has exactly 4 runs).

5, 9, 10, 11, 13, 17, 18, 19, 20, 22, 23, 25, 26, 27, 29, 33, 34, 35, 36, 38, 39, 40, 44, 46, 47, 49, 50, 51, 52, 54, 55, 57, 58, 59, 61, 65, 66, 67, 68, 70, 71, 72, 76, 78, 79, 80, 88, 92, 94, 95, 97, 98, 99, 100, 102, 103, 104, 108, 110

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base

Comments

Numbers with exactly two runs of 1's in binary. - Franklin T. Adams-Watters, Dec 09 2013

Crossrefs

Cf. A023758, A043683, A043684, A043685, A043686.

Programs

Mathematica

Select[Range[250],Length[Split[IntegerDigits[#,2]]]==4&]/2 (* Harvey P. Dale, Aug 25 2016 *)

PARI

runs(n)=my(s);while(n, n>>=valuation(if(n%2,n+1,n),2);s++); s
is(n)=runs(n>>valuation(n,2))==3 \\ Charles R Greathouse IV, Dec 09 2013