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A291269
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Numbers that contain exactly 2 pairs of identical digits.
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1
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1001, 1010, 1100, 1122, 1133, 1144, 1155, 1166, 1177, 1188, 1199, 1212, 1221, 1313, 1331, 1414, 1441, 1515, 1551, 1616, 1661, 1717, 1771, 1818, 1881, 1919, 1991, 2002, 2020, 2112, 2121, 2200, 2211, 2233, 2244, 2255, 2266, 2277, 2288, 2299, 2323, 2332, 2424, 2442
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OFFSET
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1,1
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COMMENTS
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Since other digits may be present, the last term is 998876543210; otherwise the last term would be 9988.
No multiples above 2 of identical digits are allowed, e.g., 1122333 is not a member of the sequence. - Harvey P. Dale, Nov 07 2021
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LINKS
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MATHEMATICA
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Select[Range[10^3, 10^4 - 1], Union@ Map[Length, #] == {2} &@ Split@ Sort@ IntegerDigits@ # &] (* Michael De Vlieger, Aug 24 2017 *)
(* program above only works for numbers of 4 digits, or *)
ok[n_] := Block[{d = DigitCount[n]}, Count[d, 2] == 2 && {} == Select[d, # > 2 &]]; Select[Range[11000], ok] (* Giovanni Resta, Aug 25 2017 *)
tpidQ[n_]:=Module[{dc=DigitCount[n]}, Max[dc]==2&&Count[dc, 2]==2]; Select[ Range[2500], tpidQ] (* Harvey P. Dale, Nov 07 2021 *)
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CROSSREFS
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KEYWORD
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nonn,base,fini
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AUTHOR
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STATUS
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approved
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