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A115939
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Numbers k such that the k-th triangular number contains each of the 10 decimal digits exactly once.
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2
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46097, 49796, 50139, 55151, 55484, 56520, 58050, 62495, 62567, 62900, 66294, 68805, 69542, 70766, 72594, 73737, 73971, 74168, 74357, 75555, 76364, 77805, 78686, 78848, 84555, 85959, 86076, 87263, 87669, 88406, 89883, 90287, 90297
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OFFSET
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1,1
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COMMENTS
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There are 82 such numbers, the largest being 138959.
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LINKS
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EXAMPLE
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T(75555) = 2854316790.
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MATHEMATICA
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Select[Range[141000], Sort[IntegerDigits[# (# + 1)/2]] == Range[0, 9] &] (* Giovanni Resta, Mar 19 2013 *)
(Sqrt[8#+1]-1)/2&/@Select[FromDigits/@Select[Permutations[Range[0, 9]], #[[1]]>0&], OddQ[Sqrt[8#+1]]&] (* Harvey P. Dale, Sep 19 2016 *)
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CROSSREFS
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KEYWORD
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nonn,base,fini,full
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AUTHOR
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STATUS
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approved
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