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A119048
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Numbers k such that the k-th triangular number contains only digits {0,1,9}.
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2
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1, 4, 13, 19, 44, 141, 195, 199, 424, 1955, 1995, 1999, 14141, 19955, 19995, 19999, 42473, 44741, 47138, 199955, 199995, 199999, 1999955, 1999995, 1999999, 4713620, 19999955, 19999995, 19999999, 199999955, 199999995, 199999999
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OFFSET
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1,2
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LINKS
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MATHEMATICA
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Select[Range[2 10^7], Complement[IntegerDigits[Binomial[# + 1, 2]], {0, 1, 9}] == {}&] (* Vincenzo Librandi, Oct 07 2015 *)
Position[Accumulate[Range[2*10^8]], _?(SubsetQ[{0, 1, 9}, IntegerDigits[ #]]&), Heads->False]//Flatten (* Harvey P. Dale, Dec 01 2018 *)
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PROG
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(Magma) [n: n in [1..2*10^7] | Set(Intseq(Binomial(n+1, 2))) subset [0, 1, 9]]; // Vincenzo Librandi, Oct 07 2015
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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