A363888 Number of divisors of 7*n-5 of form 7*k+4.

0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 1, 2, 0, 0, 0, 2, 0, 0, 0, 2, 0, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 2, 0, 0, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 2, 2, 0, 2, 0, 2, 0, 0, 0, 2, 0, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 4, 2, 0, 0, 2, 0, 0, 1, 2, 0, 0, 0, 4, 0, 0, 0, 2, 0

Offset

1,7

Links

Table of n, a(n) for n=1..100.

Formula

a(n) = A363806(7*n-5).

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

Mathematica

a[n_] := DivisorSum[7*n - 5, 1 &, Mod[#, 7] == 4 &]; Array[a, 100] (* Amiram Eldar, Jun 26 2023 *)

Prog

(PARI) a(n) = sumdiv(7*n-5, d, d%7==4);

Crossrefs

Cf. A363852, A363857, A363887.

Cf. A363806.

Sequence in context: A363860 A087623 A265260 * A338268 A269243 A036274

Adjacent sequences: A363885 A363886 A363887 * A363889 A363890 A363891

Keyword

nonn

Author

Seiichi Manyama, Jun 26 2023

Status

approved