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%I #26 Mar 13 2021 17:04:12
%S 4,8,36,44,72,76,328,332,396,400,652,656,684,692,2952,2960,2988,2992,
%T 3568,3572,3600,3608,5868,5876,5904,5908,6160,6164,6228,6232,26572,
%U 26576,26640,26644,26896,26900,26928,26936,32112,32120
%N Every run of digits of n in base 3 has length 2.
%C See A043291 for the base 2 version (which has a very simple formula), A033002 - A033014 for bases 4 through 16, A033015 - A033029 for the variants with runs of length >= 2. - _M. F. Hasler_, Feb 01 2014
%H Vincenzo Librandi, <a href="/A033001/b033001.txt">Table of n, a(n) for n = 1..250</a>
%F a(n)=4*A043307(n). - _M. F. Hasler_, Feb 01 2014
%t Select[Range[10000], Union[Length/@Split[IntegerDigits[#, 3]]]=={2}&] (* _Vincenzo Librandi_, Feb 05 2014 *)
%o From _M. F. Hasler_, Feb 01 2014 (Start)
%o (PARI) is_A033001(n)=!until(!n\=9,bittest(4588304,n%27)||return)
%o (PARI) for(n=1,9999,is_A033001(n)&&print1(n",")) \\ (End)
%o (PARI) a(n) = my(v=binary(n+1)); v[1]=0; for(i=2,#v, v[i]+=(v[i]>=v[i-1])); 4*fromdigits(v,9); \\ _Kevin Ryde_, Mar 13 2021
%K nonn,base
%O 1,1
%A _Clark Kimberling_
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