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A229262
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Smallest triangular number whose decimal expansion ends (nontrivially) with the n-th triangular number.
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1
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21, 153, 36, 210, 2415, 3321, 528, 136, 2145, 3655, 666, 378, 1891, 6105, 205120, 185136, 10153, 399171, 63190, 78210, 364231, 5253, 210276, 180300, 11325, 406351, 1378, 81406, 357435, 4465, 215496, 18528, 12561, 413595, 57630, 84666, 65703, 3741, 220780
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(4)=210 because 210 is the smallest triangular number that ends with 4th triangular number i.e. 10.
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MATHEMATICA
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TriangularQ[n_Integer?Positive] := IntegerQ[Sqrt[8*n + 1]]; f[n_] := (k = 1; While[a = ToExpression[ ToString[k] <> ToString[n]]; ! TriangularQ[a], k++ ]; a); Table[f[ n*(n + 1)/2], {n, 1, 50}]
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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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