A363855 - OEIS

%I #15 Jun 25 2023 09:41:43

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

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

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

%N Number of divisors of 7*n-3 of form 7*k+6.

%C Also number of divisors of 7*n-3 of form 7*k+3.

%F a(n) = A363805(7*n-3) = A363808(7*n-3).

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

%F G.f.: Sum_{k>0} x^(6*k-3)/(1 - x^(7*k-4)).

%t a[n_] := DivisorSum[7*n - 3, 1 &, Mod[#, 7] == 6 &]; Array[a, 100] (* _Amiram Eldar_, Jun 25 2023 *)

%o (PARI) a(n) = sumdiv(7*n-3, d, d%7==6);

%Y Cf. A361691, A363854, A363856, A363857, A363858.

%Y Cf. A363805, A363808.

%K nonn

%O 1,9

%A _Seiichi Manyama_, Jun 24 2023