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A039656
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Becomes prime after n iterations of f(x) = sigma(x)-1 (least inverse of A039655).
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9
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2, 6, 4, 27, 12, 9, 121, 301, 930, 484, 578, 441, 1273, 468, 4863, 3171, 9216, 8373, 19692, 19416, 25442, 13440, 19230, 16641, 16804, 83161, 100652, 226181, 203400, 133200, 419248, 380979, 744796, 553296, 634710, 539476, 505584, 674416, 634206
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OFFSET
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0,1
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COMMENTS
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Records: 2, 6, 27, 121, 301, 930, 1273, 4863, 9216, 19692, 25442, 83161, 100652, 226181, 419248, 744796, 3739690, 4238314, etc. - Robert G. Wilson v, Sep 23 2017
Indices of records: 0, 1, 3, 6, 7, 8, 12, 14, 16, 18, 20, 25, 26, 27, 30, 32, 46, 47, 48, 49, 50, 56, 57, 58, 59, 61, 63, 65, 67, 76, 77, 78, 82, 83, 84, 85, etc. - Robert G. Wilson v, Sep 23 2017
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LINKS
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MATHEMATICA
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f[n_] := Plus @@ Divisors@ n -1; g[n_] := Length@ NestWhileList[f@# &, n, !PrimeQ@# &] - 1; t[_] := -1; k = 2; While[k < 10000001, a = g[k]; If[ t@ a == -1, t@ a = k; Print[{a, k}]]; k++]; t@# & /@ Range[0, 50] (* Robert G. Wilson v, Sep 22 2017 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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