A363853 Number of divisors of 7*n-6 of form 7*k+1.

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

Offset: 1

Author

Seiichi Manyama, Jun 24 2023

Keywords

• nonn

Crossrefs

Cf. A359212, A359238, A359309.

Cf. A279061.

Programs

Mathematica

a[n_] := DivisorSum[7*n - 6, 1 &, Mod[#, 7] == 1 &]; Array[a, 100] (* Amiram Eldar, Jun 25 2023 *)

PARI

a(n) = sumdiv(7*n-6, d, d%7==1);

Formula

a(n) = A279061(7*n-6).

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