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A238905
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The tau(sigma)-perfect numbers, where the set of f-perfect numbers for an arithmetical function f is defined in A066218.
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1
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6, 15, 22, 33, 39, 57, 69, 111, 129, 141, 183, 201, 214, 219, 237, 309, 453, 471, 489, 573, 579, 633, 669, 813, 831, 849, 939, 993, 1101, 1149, 1191, 1263, 1371, 1389, 1461, 1519, 1569, 1623, 1641, 1821, 1839, 1893, 1942, 1983, 2019, 2073, 2199, 2253, 2271
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OFFSET
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1,1
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LINKS
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EXAMPLE
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Aliquot divisors of 39 are 1, 3, 13. Then tau(sigma(1)) + tau(sigma(3)) + tau(sigma(13)) = 1 + 3 + 4 = 8 and tau(sigma(39)) = 8.
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MAPLE
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with(numtheory); P:=proc(q) local a, b, i, n;
for n from 1 to q do a:=divisors(n); b:=0;
for i from 1 to nops(a)-1 do b:=b+tau(sigma(a[i])); od;
if tau(sigma(n))=b then print(n); fi; od; end: P(10^6);
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MATHEMATICA
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q[n_] := DivisorSum[n, DivisorSigma[0, DivisorSigma[1, #]] &, # < n &] == DivisorSigma[0, DivisorSigma[1, n]]; Select[Range[2300], q] (* Amiram Eldar, Aug 22 2023 *)
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PROG
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(PARI) isok(n) = numdiv(sigma(n)) == sumdiv(n, d, (d<n)*numdiv(sigma(d))); \\ Michel Marcus, Mar 08 2014
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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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