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%I #10 Sep 08 2022 08:45:08
%S -1,0,2,8,6,30,10,53,46,98,18,158,22,198,180,252,30,383,34,446,340,
%T 494,42,722,242,690,480,870,54,1172,58,1073,804,1178,708,1686,70,1470,
%U 1108,1890,78,2292,82,2126,1754,2150,90,3054,678,2819,1860,2958,102,3712,1556,3610
%N a(n) = sigma[k](n) - phi(n)^k - d(n)^k for k=2.
%C It is known that a(n) >= 0 for n >= 2.
%D D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, p. 10.
%H T. D. Noe, <a href="/A079538/b079538.txt">Table of n, a(n) for n=1..10000</a>
%F a(n) = 2*n - 4 for prime n. - _T. D. Noe_, Dec 19 2006
%t Table[DivisorSigma[2,n] - EulerPhi[n]^2 - DivisorSigma[0, n]^2, {n, 80}] (* _G. C. Greubel_, Jan 15 2019 *)
%o (PARI) vector(80, n, sigma(n,2) - eulerphi(n)^2 - numdiv(n)^2) \\ _G. C. Greubel_, Jan 15 2019
%o (Magma) [DivisorSigma(2,n) - EulerPhi(n)^2 - DivisorSigma(0,n)^2: n in [1..80]]; // _G. C. Greubel_, Jan 15 2019
%o (Sage) [sigma(n,2) - euler_phi(n)^2 - sigma(n,0)^2 for n in (1..80)] # _G. C. Greubel_, Jan 15 2019
%Y Cf. A000010, A000005, A000203, A046520 (for k=1), A079539.
%K sign
%O 1,3
%A _N. J. A. Sloane_, Jan 23 2003
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