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 A031955 #49 Oct 12 2021 07:56:08
%S A031955 10,12,13,14,15,16,17,18,19,20,21,23,24,25,26,27,28,29,30,31,32,34,35,
%T A031955 36,37,38,39,40,41,42,43,45,46,47,48,49,50,51,52,53,54,56,57,58,59,60,
%U A031955 61,62,63,64,65,67,68,69,70,71,72,73,74,75,76,78,79,80,81,82,83,84,85,86,87,89,90,91,92,93,94,95,96,97,98,100,101,110,112,113,114,115,116,117,118,119,121,122,131,133,141,144,151,155,161,166
%N A031955 Numbers with exactly two distinct base-10 digits.
%C A031955 The three-digit terms are given by A210666(1,...,244). For numbers with exactly two distinct (but unspecified) digits in other bases, see A031948-A031954. For numbers made of two *given* digits, see A007088 (digits 0 & 1), A007931 (digits 1 & 2), A032810 (digits 2 & 3), A032834 (digits 3 & 4), A256290 (digits 4 & 5), A256291 (digits 5 & 6), A256292 (digits 6 & 7), A256340 (digits 7 & 8), A256341 (digits 8 & 9), and A032804-A032816 (in other bases). - _M. F. Hasler_, Apr 04 2015
%C A031955 A235154 is a subsequence. - _Altug Alkan_, Dec 03 2015
%C A031955 A235717 is a subsequence. - _Robert Israel_, Dec 03 2015
%H A031955 Reinhard Zumkeller, <a href="/A031955/b031955.txt">Table of n, a(n) for n = 1..10000</a>
%H A031955 <a href="/index/Ar#10-automatic">Index entries for 10-automatic sequences</a>.
%F A031955 A043537(a(n)) = 2. - _Reinhard Zumkeller_, Dec 03 2009
%p A031955 M:= 5: # to get all terms < 10^M
%p A031955 sort([seq(seq(seq(seq(add(10^(m-j)*`if`(member(j,S2),d2,d1),j=1..m) ,
%p A031955 S2 = combinat:-powerset({$2..m}) minus {{}}),
%p A031955 d2 = {$0..9} minus {d1}), d1 = 1..9), m=2..M)]); # _Robert Israel_, Dec 03 2015
%t A031955 Select[Range@ 166, Length@ Union@ IntegerDigits@ # == 2 &] (* _Michael De Vlieger_, Dec 03 2015 *)
%o A031955 (Haskell)
%o A031955 a031955 n = a031955_list !! (n-1)
%o A031955 a031955_list = filter ((== 2) . a043537) [0..]
%o A031955 -- _Reinhard Zumkeller_, Feb 05 2012
%o A031955 (PARI) is_A031955(n)=#Set(digits(n))==2 \\ _M. F. Hasler_, Apr 04 2015
%o A031955 (Python)
%o A031955 def ok(n): return len(set(str(n))) == 2
%o A031955 print(list(filter(ok, range(167)))) # _Michael S. Branicky_, Oct 12 2021
%Y A031955 Different from A029742.
%Y A031955 Cf. A043638, A101594, A031948, A031949, A031950, A031951, A031952, A031953, A031954, A235154, A235717.
%K A031955 nonn,base,easy
%O A031955 1,1
%A A031955 _Clark Kimberling_
%E A031955 Name edited by _Charles R Greathouse IV_, Feb 13 2017