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A363851
Number of divisors of 7*n-4 of form 7*k+1.
0
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.
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
Sequence in context: A103956 A103957 A232550 * A305426 A322811 A091853
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 24 2023
STATUS
approved