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A359241
Number of divisors of 5*n-4 of form 5*k+4.
7
0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 2, 1, 0, 0, 2, 0, 0, 0, 2, 0, 2, 0, 2, 0, 0, 0, 2, 0, 0, 2, 2, 0, 0, 0, 3, 0, 0, 0, 4, 0, 0, 0, 2, 0, 0, 0, 2, 2, 2, 0, 2, 0, 0, 0, 2, 0, 2, 0, 2, 0, 0, 0, 4, 0, 0, 2, 2, 1, 0, 0, 2, 0, 0, 0, 4, 0, 2, 0, 2, 0, 0, 0, 2, 2, 0
OFFSET
1,8
LINKS
FORMULA
a(n) = A001899(5*n-4).
G.f.: Sum_{k>0} x^(4*k)/(1 - x^(5*k-1)).
MATHEMATICA
a[n_] := DivisorSum[5*n-4, 1 &, Mod[#, 5] == 4 &]; Array[a, 100] (* Amiram Eldar, Aug 23 2023 *)
PROG
(PARI) a(n) = sumdiv(5*n-4, d, d%5==4);
(PARI) my(N=100, x='x+O('x^N)); concat([0, 0, 0], Vec(sum(k=1, N, x^(4*k)/(1-x^(5*k-1)))))
CROSSREFS
Cf. A001899.
Sequence in context: A338268 A269243 A036274 * A047753 A303947 A031123
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 22 2022
STATUS
approved