%I #8 Sep 08 2022 08:45:08

%S 0,0,2,4,5,8,10,8,14,16,16,20,29,32,26,28,32,48,34,40,38,40,66,44,69,

%T 56,50,88,64,56,58,112,108,64,80,68,70,116,144,76,149,80,148,104,86,

%U 176,112,168,94,204,98,100,192,104,106,136,110,208,250,240,197,152,244,124,160

%N a(n) = phi(2*n+1)*d(2*n+1) - sigma(2*n+1).

%C It is known that a(n) >= 0.

%D D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, p. 10.

%H G. C. Greubel, <a href="/A079537/b079537.txt">Table of n, a(n) for n = 0..10000</a>

%t Table[EulerPhi[2*n+1]*DivisorSigma[0, 2*n+1] - DivisorSigma[1, 2*n+1], {n, 0, 80}] (* _G. C. Greubel_, Jan 15 2019 *)

%o (PARI) vector(80, n, n--; eulerphi(2*n+1)*sigma(2*n+1,0) - sigma(2*n+1,1)) \\ _G. C. Greubel_, Jan 15 2019

%o (Magma) [EulerPhi(2*n+1)*DivisorSigma(0,2*n+1) - DivisorSigma(1,2*n+1): n in [0..80]]; // _G. C. Greubel_, Jan 15 2019

%o (Sage) [euler_phi(2*n+1)*sigma(2*n+1, 0) - sigma(2*n+1,1) for n in (0..80)] # _G. C. Greubel_, Jan 15 2019

%Y Cf. A000010, A000005, A000203, A079536.

%K nonn

%O 0,3

%A _N. J. A. Sloane_, Jan 23 2003