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A066294
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a(n) = A000203(n)^2 - A001157(n) - 2n = sigma(n)^2 - sigma_2(n) - 2n.
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1
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-2, 0, 0, 20, 0, 82, 0, 124, 60, 174, 0, 550, 0, 298, 286, 588, 0, 1030, 0, 1178, 482, 642, 0, 2702, 260, 862, 726, 2030, 0, 3824, 0, 2540, 1018, 1398, 934, 6298, 0, 1714, 1358, 5810, 0, 6632, 0, 4406, 3628, 2442, 0, 11870, 700, 5294, 2182, 5930, 0, 10192, 1902, 10038, 2666, 3774, 0, 22644, 0, 4282, 6140, 10540, 2506
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OFFSET
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1,1
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COMMENTS
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For primes p, a(p) = 0, otherwise positive, except for n = 1 where it is negative.
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LINKS
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MATHEMATICA
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a[n_] := DivisorSigma[1, n]^2 - DivisorSigma[2, n] - 2n; Array[a, 65] (* Amiram Eldar, Jul 31 2019 *)
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PROG
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(PARI) a(n) = sigma(n)^2 - sigma(n, 2) - 2*n; \\ Michel Marcus, Mar 22 2020
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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