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A113466
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Least number that begins an n-term arithmetic progression with common difference 2 in which all terms have the same number of divisors.
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2
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1, 3, 3, 213, 213, 1383, 3091, 8129, 943607, 943607, 19235031, 21470685, 21470685, 21470685, 21470685
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OFFSET
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1,2
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COMMENTS
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Second column of A113465. Next term is > 6368300000.
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LINKS
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EXAMPLE
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a(4) = 213 because 213, 215, 217 and 219 each have 4 divisors.
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MATHEMATICA
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Module[{nn=21470695, ds}, ds=Table[DivisorSigma[0, n], {n, 1, nn, 2}]; 2*Table[ SequencePosition[ds, PadRight[{}, k, x_], 1], {k, 15}][[All, 1]]][[All, 1]]-1 (* Requires Mathematica version 10 or later *) (* The program will take a long time to run. To generate the first 8 terms of the sequence, change the nn constant to 8200 and the k range from 15 to 8 and the program will run quickly. *) (* Harvey P. Dale, Aug 16 2020 *)
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CROSSREFS
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KEYWORD
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nonn,less,hard
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AUTHOR
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STATUS
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approved
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