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 A043631 #19 Aug 29 2025 16:14:57
%S A043631 9,11,12,13,14,15,16,17,18,19,21,22,23,24,25,26,27,28,29,31,32,33,34,
%T A043631 35,36,37,38,39,41,42,43,44,45,46,47,48,49,51,52,53,54,55,56,57,58,59,
%U A043631 61,62,63,64,65,66,67,68,69,71,72,73,74,75,76,77,78,79,81,90,92,93,94,95
%N A043631 Numbers whose base-9 representation has exactly 2 runs.
%H A043631 Harvey P. Dale, <a href="/A043631/b043631.txt">Table of n, a(n) for n = 1..1000</a>
%p A043631 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
%t A043631 Select[Range[100],Length[Split[IntegerDigits[#,9]]]==2&] (* _Harvey P. Dale_, Jan 06 2022 *)
%Y A043631 Cf. A007095.
%Y A043631 Subsequence of A043698.
%K A043631 nonn,base,changed
%O A043631 1,1
%A A043631 _Clark Kimberling_
%E A043631 Extended by _R. J. Mathar_, Oct 20 2008