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A359227
Number of divisors of 4*n-3 of form 4*k+1.
4
1, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 4, 2, 2, 2, 2, 4, 2, 2, 2, 3, 4, 2, 2, 2, 2, 4, 2, 2, 4, 2, 4, 2, 2, 2, 2, 4, 2, 4, 2, 2, 4, 3, 2, 2, 2, 4, 4, 2, 2, 2, 4, 2, 2, 2, 4, 6, 2, 2, 2, 2, 4, 2, 2, 2, 4, 4, 2, 4, 2, 2, 4, 3, 2, 4, 2, 4, 2, 2, 2, 2, 6, 2, 4, 2, 2, 4, 2, 2, 4
OFFSET
1,2
FORMULA
a(n) = A001826(4*n-3).
G.f.: Sum_{k>0} x^k/(1 - x^(4*k-3)).
MATHEMATICA
a[n_] := DivisorSum[4*n-3, 1 &, Mod[#, 4] == 1 &]; Array[a, 100] (* Amiram Eldar, Aug 23 2023 *)
PROG
(PARI) a(n) = sumdiv(4*n-3, d, d%4==1);
(PARI) my(N=100, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-x^(4*k-3))))
CROSSREFS
Sequence in context: A187188 A358618 A183027 * A078178 A306396 A355035
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Dec 22 2022
STATUS
approved