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a(n) = (1/24)*(sigma_3(2*n-1) - sigma_1(2*n-1)).
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%I #15 Jan 04 2025 06:20:30

%S 0,1,5,14,31,55,91,146,204,285,400,506,655,850,1015,1240,1552,1804,

%T 2109,2562,2870,3311,3971,4324,4914,5730,6201,6990,8000,8555,9455,

%U 10846,11536,12529,14192,14910,16206,18371,19088,20540,22990,23821,25794

%N a(n) = (1/24)*(sigma_3(2*n-1) - sigma_1(2*n-1)).

%H Harvey P. Dale, <a href="/A081861/b081861.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = (A045823(n-1) - A008438(n-1)) / 24. - _Amiram Eldar_, Jan 04 2025

%t Table[(DivisorSigma[3,2n-1]-DivisorSigma[1,2n-1])/24,{n,50}] (* _Harvey P. Dale_, Dec 15 2012 *)

%o (PARI) a(n) = my(f = factor(2*n-1)); (sigma(f, 3) - sigma(f)) / 24; \\ _Amiram Eldar_, Jan 04 2025

%Y Cf. A000203, A001158, A008438, A045823, A081863(1).

%K nonn,easy

%O 1,3

%A _Benoit Cloitre_, Apr 11 2003