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0, 8, 12, 45, 20, 140, 28, 209, 133, 308, 44, 768, 52, 540, 512, 897, 68, 1485, 76, 1700, 880, 1196, 92, 3536, 561, 1620, 1276, 2992, 116, 5120, 124, 3713, 1904, 2660, 1728, 8137, 148, 3276, 2560, 7844, 164, 9072, 172, 6656, 5508, 4700, 188, 15120, 1485
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listen;
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internal format)
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OFFSET
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1,2
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COMMENTS
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If n is prime, then a(n) = 4n.
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LINKS
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FORMULA
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Sum_{k=1..n} a(k) ~ c * n^3 / 3, where c = 5*zeta(3)/2 - Product_{p prime}(1 - (2*p-1)/p^3) = (5/2)*A002117 - A065464 = 2.576892... . (End)
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MATHEMATICA
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Table[DivisorSigma[1, n]^2-EulerPhi[n]^2, {n, 50}] (* Harvey P. Dale, Nov 08 2013 *)
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PROG
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CROSSREFS
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Cf. A000010, A000203, A002117, A051612, A062354, A065387, A065464, A072861, A077099, A077100, A127473.
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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