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%I #10 Jun 25 2023 10:40:59
%S 0,0,1,0,0,0,1,1,0,0,1,0,1,0,1,0,0,1,2,0,0,0,2,0,0,0,1,1,0,1,2,0,1,0,
%T 1,0,0,1,1,0,1,0,3,0,0,0,1,1,1,0,1,1,1,0,2,0,0,1,1,0,0,0,3,0,0,0,3,2,
%U 0,0,1,0,1,1,1,0,0,1,2,0,0,0,2,0,2,0,2,1,0,0,2,0,2,0,1,1,0,1,1,0
%N Number of divisors of 7*n-1 of form 7*k+4.
%C Also number of divisors of 7*n-1 of form 7*k+5.
%F a(n) = A363806(7*n-1) = A363807(7*n-1).
%F G.f.: Sum_{k>0} x^(5*k-2)/(1 - x^(7*k-3)).
%F G.f.: Sum_{k>0} x^(4*k-1)/(1 - x^(7*k-2)).
%t a[n_] := DivisorSum[7*n - 1, 1 &, Mod[#, 7] == 4 &]; Array[a, 100] (* _Amiram Eldar_, Jun 25 2023 *)
%o (PARI) a(n) = sumdiv(7*n-1, d, d%7==4);
%Y Cf. A363806, A363807.
%K nonn
%O 1,19
%A _Seiichi Manyama_, Jun 24 2023