A363877 - OEIS

%I #11 Jun 25 2023 10:40:51

%S 0,1,0,0,1,1,0,1,0,1,1,0,0,2,0,1,1,1,0,1,0,1,1,0,0,3,1,0,1,1,0,1,0,1,

%T 1,1,0,3,0,0,1,1,0,2,0,2,1,0,1,2,0,0,1,1,0,2,0,1,1,1,1,3,0,0,1,2,0,1,

%U 0,1,2,0,0,2,0,1,1,2,0,2,0,2,1,0,0,4,0,0,1,1,0,1,1,1,2,1,0,3,0,0

%N Number of divisors of 7*n-2 of form 7*k+3.

%C Also number of divisors of 7*n-2 of form 7*k+4.

%F a(n) = A363805(7*n-2) = A363806(7*n-2).

%F G.f.: Sum_{k>0} x^(4*k-2)/(1 - x^(7*k-4)).

%F G.f.: Sum_{k>0} x^(3*k-1)/(1 - x^(7*k-3)).

%t a[n_] := DivisorSum[7*n - 2, 1 &, Mod[#, 7] == 3 &]; Array[a, 100] (* _Amiram Eldar_, Jun 25 2023 *)

%o (PARI) a(n) = sumdiv(7*n-2, d, d%7==3);

%Y Cf. A363805, A353806.

%K nonn

%O 1,14

%A _Seiichi Manyama_, Jun 25 2023