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a(0)=1; a(n) = sigma_1(n) + sigma_2(n) + sigma_3(n).
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%I #13 Dec 16 2024 02:00:18

%S 1,3,17,42,101,158,314,402,685,861,1282,1466,2282,2382,3370,3812,5053,

%T 5222,7307,7242,9786,10164,12634,12722,17290,16433,20674,21300,26218,

%U 25262,33124,30786,38877,38564,45730,44692,57263,52062,63610,63300,76010,70646,89284

%N a(0)=1; a(n) = sigma_1(n) + sigma_2(n) + sigma_3(n).

%H Amiram Eldar, <a href="/A092347/b092347.txt">Table of n, a(n) for n = 0..10000</a>

%t a[0] = 1; a[n_] := Total[DivisorSigma[{1, 2, 3}, n]]; Array[a, 50, 0] (* _Amiram Eldar_, Dec 16 2024 *)

%o (PARI) a(n) = if(n == 0, 1, sum(k = 1, 3, sigma(n, k))); \\ _Amiram Eldar_, Dec 16 2024

%Y Cf. A000203, A001157, A001158.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_, Mar 20 2004