A043631 Numbers whose base-9 representation has exactly 2 runs.

9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 48, 49, 51, 52, 53, 54, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 90, 92, 93, 94, 95

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• base
• changed

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A007095.

Subsequence of A043698.

Programs

Maple

rlen := proc(n,ba) local rs,s,dgs,i ; rs :=0 ; s := 0; dgs := convert(n,base,ba) ; for i from 1 to nops(dgs) do if s = 0 then s :=1 ; else if op(i,dgs) <> op(i-1,dgs) then rs := rs+1 ; s :=1 ; else s :=s+1 ; fi; fi; od: rs := rs+1 ; RETURN (rs) ; end: for n from 1 to 200 do if rlen(n,9) = 2 then printf("%d,",n) ; fi; od: # R. J. Mathar, Oct 20 2008

Mathematica

Select[Range[100],Length[Split[IntegerDigits[#,9]]]==2&] (* Harvey P. Dale, Jan 06 2022 *)

Extensions

Extended by R. J. Mathar, Oct 20 2008