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%I #13 Aug 23 2023 08:42:11
%S 1,2,2,2,2,3,2,2,2,4,2,2,2,4,2,2,3,4,2,2,2,4,2,4,2,4,2,2,2,4,4,2,2,5,
%T 2,2,2,6,2,2,2,4,2,4,4,4,2,2,2,4,2,4,2,6,2,2,3,4,4,2,2,4,2,4,2,6,2,2,
%U 2,6,2,2,4,6,2,2,2,4,2,4,2,4,4,4,2,5,4,2,2,4
%N Number of divisors of 3*n-2 of form 3*k+1.
%F G.f.: Sum_{k>0} x^k/(1 - x^(3*k-2)).
%t a[n_] := DivisorSum[3*n-2, 1 &, Mod[#, 3] == 1 &]; Array[a, 100] (* _Amiram Eldar_, Aug 23 2023 *)
%o (PARI) a(n) = sumdiv(3*n-2, d, d%3==1);
%o (PARI) my(N=100, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-x^(3*k-2))))
%Y Cf. A001817, A359211.
%K nonn,easy
%O 1,2
%A _Seiichi Manyama_, Dec 21 2022
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