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%I #11 Sep 08 2022 08:45:08
%S 0,-1,0,-1,2,-4,4,1,5,-2,8,-4,10,0,8,9,14,-3,16,6,16,4,20,4,29,6,32,
%T 16,26,-8,28,33,32,10,48,17,34,12,40,38,38,0,40,36,66,16,44,36,69,27,
%U 56,46,50,24,88,72,64,22,56,24,58,24,112,97,108,16,64,66,80,48,68,93,70,30,116,76,144
%N a(n) = phi(n)*d(n) - sigma(n).
%C It is known that a(n) >= 0 if n is odd
%D D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, p. 10.
%H G. C. Greubel, <a href="/A079536/b079536.txt">Table of n, a(n) for n = 1..10000</a>
%t Table[EulerPhi[n]*DivisorSigma[0, n] - DivisorSigma[1, n], {n,1,80}] (* _G. C. Greubel_, Jan 14 2019 *)
%o (PARI) vector(80, n, eulerphi(n)*sigma(n,0) - sigma(n,1)) \\ _G. C. Greubel_, Jan 14 2019
%o (Magma) [EulerPhi(n)*DivisorSigma(0,n) - DivisorSigma(1,n): n in [1..80]]; // _G. C. Greubel_, Jan 14 2019
%o (Sage) [euler_phi(n)*sigma(n, 0) - sigma(n,1) for n in (1..80)] # _G. C. Greubel_, Jan 14 2019
%Y Cf. A000010, A000005, A000203, A062355, A079535, A079537.
%K sign
%O 1,5
%A _N. J. A. Sloane_, Jan 23 2003
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