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 A031955 Numbers with exactly two distinct base 10 digits. 9
 10, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 56, 57, 58, 59, 60, 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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 A235154 is a subsequence. - Altug Alkan, Dec 03 2015 A235717 is a subsequence. - Robert Israel, Dec 03 2015 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 FORMULA A043537(a(n)) = 2. - Reinhard Zumkeller, Dec 03 2009 MAPLE M:= 5: # to get all terms < 10^M sort([seq(seq(seq(seq(add(10^(m-j)*`if`(member(j, S2), d2, d1), j=1..m)  ,   S2 = combinat:-powerset({\$2..m}) minus {{}}),   d2 = {\$0..9} minus {d1}), d1 = 1..9), m=2..M)]); # Robert Israel, Dec 03 2015 MATHEMATICA Select[Range@ 166, Length@ Union@ IntegerDigits@ # == 2 &] (* Michael De Vlieger, Dec 03 2015 *) PROG (Haskell) a031955 n = a031955_list !! (n-1) a031955_list = filter ((== 2) . a043537) [0..] -- Reinhard Zumkeller, Feb 05 2012 (PARI) is_A031955(n)=#Set(digits(n))==2 \\ M. F. Hasler, Apr 04 2015 CROSSREFS Different from A029742. Cf. A043638, A101594, A031948, A031949, A031950, A031951, A031952, A031953, A031954, A235154, A235717. Sequence in context: A139704 A139819 A288040 * A029742 A043638 A280824 Adjacent sequences:  A031952 A031953 A031954 * A031956 A031957 A031958 KEYWORD nonn,base,easy AUTHOR EXTENSIONS Name edited by Charles R Greathouse IV, Feb 13 2017 STATUS approved

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Last modified October 19 13:01 EDT 2019. Contains 328222 sequences. (Running on oeis4.)