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A097702
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a(n) = (A063880(n) - 108)/216.
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3
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0, 2, 3, 5, 6, 8, 9, 11, 14, 15, 17, 18, 20, 21, 23, 26, 27, 29, 30, 32, 33, 35, 36, 38, 39, 41, 42, 44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 63, 65, 66, 68, 69, 71, 72, 74, 75, 77, 78, 80, 81, 83, 86, 89, 90, 92, 93, 95, 96, 98, 99, 101, 102, 104, 105, 107, 108, 110
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OFFSET
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1,2
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COMMENTS
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Conjecture: n is a member iff 6*n+3 is squarefree. - Vladeta Jovovic, Aug 27 2004
It is only a conjecture that all terms are integers (confirmed up to 10^6 by Robert G. Wilson v).
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LINKS
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MATHEMATICA
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usigma[n_] := Block[{d = Divisors[n]}, Plus @@ Select[d, GCD[ #, n/# ] == 1 &]]; (Select[ Range[ 24500], DivisorSigma[1, # ] == 2usigma[ # ] &] - 108)/216 (* Robert G. Wilson v, Aug 28 2004 *)
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PROG
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(PARI) {u(n)=sumdiv(n, d, if(gcd(d, n/d)==1, d))} n=2:while(1, n++: if(sigma(n)==2*u(n), print1((n-108)/216", ")))
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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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