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Every run of digits of n in base 10 has length 2.
4

%I #11 Feb 05 2014 08:09:26

%S 11,22,33,44,55,66,77,88,99,1100,1122,1133,1144,1155,1166,1177,1188,

%T 1199,2200,2211,2233,2244,2255,2266,2277,2288,2299,3300,3311,3322,

%U 3344,3355,3366,3377,3388,3399,4400,4411,4422,4433

%N Every run of digits of n in base 10 has length 2.

%C See A043291 and A033001 through A033014 for the analog in other bases, A033015 - A033029 for the variants with run lengths >= 2. - _M. F. Hasler_, Feb 02 2014

%H Vincenzo Librandi, <a href="/A033008/b033008.txt">Table of n, a(n) for n = 1..800</a>

%F a(n) = 11*A043314(n) (= 11*n for n<10). - _M. F. Hasler_, Feb 02 2014

%t Select[Range[10000], Union[Length/@Split[IntegerDigits[#, 10]]]=={2}&] (* _Vincenzo Librandi_, Feb 05 2014 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_