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A055033
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a(n) = usigma(usigma(n)), where usigma(n) is the sum of unitary divisors of n (A034448).
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2
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1, 4, 5, 6, 12, 20, 9, 10, 18, 30, 20, 30, 24, 36, 36, 18, 30, 72, 30, 72, 33, 50, 36, 50, 42, 96, 40, 54, 72, 90, 33, 48, 68, 84, 68, 78, 60, 120, 72, 84, 96, 132, 60, 120, 120, 90, 68, 90, 78, 168, 90, 144, 84, 160, 90, 90, 102, 180, 120, 216, 96
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OFFSET
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1,2
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LINKS
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FORMULA
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MATHEMATICA
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usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); usigma[1] = 1; a[n_] := usigma[usigma[n]]; Array[a, 100] (* Amiram Eldar, Jul 24 2024 *)
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PROG
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(PARI) usigma(n) = {my(f = factor(n)); prod(i = 1, #f~, 1 + f[i, 1]^f[i, 2]); }
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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