A363860 Number of divisors of 7*n-1 of form 7*k+4.

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, 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, 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

Offset: 1

Author

Seiichi Manyama, Jun 24 2023

Keywords

• nonn

Comments

Also number of divisors of 7*n-1 of form 7*k+5.

Crossrefs

Cf. A363806, A363807.

Programs

Mathematica

a[n_] := DivisorSum[7*n - 1, 1 &, Mod[#, 7] == 4 &]; Array[a, 100] (* Amiram Eldar, Jun 25 2023 *)

PARI

a(n) = sumdiv(7*n-1, d, d%7==4);

Formula

a(n) = A363806(7*n-1) = A363807(7*n-1).

G.f.: Sum_{k>0} x^(5*k-2)/(1 - x^(7*k-3)).

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