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A322486
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Semi-unitary perfect numbers: numbers k such that susigma(k) = 2k, where susigma(k) is the sum of the semi-unitary divisors of k (A322485).
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5
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6, 60, 90, 264, 3960, 4560, 8736, 13770, 131040, 384384, 605880, 5765760, 20049120, 882161280, 23253135360
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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264 is in the sequence since its sum of semi-unitary divisors is susigma(264) = 528 = 2 * 264.
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MATHEMATICA
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f[p_, e_] := (p^Floor[(e+1)/2] - 1)/(p-1) + p^e; susigma[n_] := If[n==1, 1, Times @@ (f @@@ FactorInteger[n])]; aQ[n_] := susigma[n]==2n; Select[Range[10000], aQ]
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PROG
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(PARI) ssu(n) = {my(f = factor(n)); for (k=1, #f~, my(p=f[k, 1], e=f[k, 2]); f[k, 1] = (p^((e+1)\2) - 1)/(p-1) + p^e; f[k, 2] = 1; ); factorback(f); } \\ A322485
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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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