A363878 - OEIS

%I #11 Jun 25 2023 10:40:36

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

%T 0,1,1,1,0,2,0,2,1,2,0,1,1,1,0,1,0,4,0,1,0,1,1,1,0,2,1,2,1,2,0,1,1,1,

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

%N Number of divisors of 7*n-4 of form 7*k+2.

%C Also number of divisors of 7*n-4 of form 7*k+5.

%F a(n) = A363795(7*n-4) = A363807(7*n-4).

%F G.f.: Sum_{k>0} x^(5*k-3)/(1 - x^(7*k-5)).

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

%t a[n_] := DivisorSum[7*n - 4, 1 &, Mod[#, 7] == 2 &]; Array[a, 100] (* _Amiram Eldar_, Jun 25 2023 *)

%o (PARI) a(n) = sumdiv(7*n-4, d, d%7==2);

%Y Cf. A363795, A363807.

%K nonn

%O 1,12

%A _Seiichi Manyama_, Jun 25 2023