A363851 Number of divisors of 7*n-4 of form 7*k+1.

1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 3, 1, 1, 2, 1, 1, 3, 1, 1, 2, 2, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1, 1, 2, 1, 1, 5, 1, 2, 2, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1, 1, 3, 2, 1, 2, 2, 2, 2, 1, 1, 4, 1, 1, 2, 1, 1, 4, 1, 2, 2, 1, 1, 3, 1, 1, 2, 3, 1, 2, 1, 1, 3, 2, 1, 4

Offset

1,4

Comments

Also number of divisors of 7*n-4 of form 7*k+3.

Links

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

Formula

a(n) = A279061(7*n-4) = A363805(7*n-4).

G.f.: Sum_{k>0} x^(3*k-2)/(1 - x^(7*k-6)).

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

Mathematica

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

Prog

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

Crossrefs

Cf. A279061, A363805.

Sequence in context: A103956 A103957 A232550 * A305426 A322811 A091853

Adjacent sequences: A363848 A363849 A363850 * A363852 A363853 A363854

Keyword

nonn

Author

Seiichi Manyama, Jun 24 2023

Status

approved