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Number of divisors of 7*n-3 of form 7*k+5.
1

%I #12 Jun 26 2023 06:33:10

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

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

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

%N Number of divisors of 7*n-3 of form 7*k+5.

%F a(n) = A363807(7*n-3).

%F G.f.: Sum_{k>0} x^(5*k-1)/(1 - x^(7*k-2)).

%t a[n_] := DivisorSum[7*n - 3, 1 &, Mod[#, 7] == 5 &]; Array[a, 100] (* _Amiram Eldar_, Jun 26 2023 *)

%o (PARI) a(n) = sumdiv(7*n-3, d, d%7==5);

%Y Cf. A363850, A363855, A363885.

%Y Cf. A363807.

%K nonn

%O 1,9

%A _Seiichi Manyama_, Jun 26 2023