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A275337
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Least k such that sigma(k*n) = sigma(k*n+1), or 0 if no such k exists.
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3
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OFFSET
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1,1
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COMMENTS
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Terms 6 through 30, with 0 signifying no such k <= 10^6: {0, 2, 220708, 1649, 23039, 87, 0, 6141, 1, 179, 110354, 873, 0, 86, 0, 5813, 62, 58, 0, 37497, 17149, 699, 0, 33, 0}. - Michael De Vlieger, Jul 25 2016
If a(n) = 0, then a(m*n) = 0 for all m > 0. If c is a divisor of a(n), then a(c*n) = a(n)/c. - Chai Wah Wu, Jul 26 2016
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LINKS
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EXAMPLE
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a(3) = 319 because sigma(319*3) = sigma(319*3+1) = 1440.
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MATHEMATICA
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Table[SelectFirst[Range[10^6], DivisorSigma[1, # n] == DivisorSigma[1, # n + 1] &], {n, 30}] /. k_ /; MissingQ@ k -> 0 (* Michael De Vlieger, Jul 25 2016, Version 10.2 *)
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PROG
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(PARI) a(n) = {my(k = 1); while (sigma(k*n) != sigma(k*n+1), k++); k; } \\ Michel Marcus, Jul 26 2016
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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