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A363514
Sum of divisors of 3*n-1 of form 3*k+1.
6
1, 1, 5, 1, 8, 1, 15, 1, 14, 1, 21, 8, 20, 1, 27, 1, 36, 1, 40, 1, 32, 14, 39, 1, 38, 8, 71, 1, 44, 1, 51, 20, 57, 1, 70, 1, 88, 1, 63, 8, 62, 26, 85, 1, 68, 1, 120, 14, 74, 1, 100, 32, 80, 8, 87, 1, 130, 1, 131, 1, 112, 38, 99, 1, 98, 1, 180, 8, 104, 20, 111, 44, 110, 14, 168, 1, 172, 1
OFFSET
1,3
LINKS
FORMULA
a(n) = A078181(3*n-1).
G.f.: Sum_{k>0} (3*k-2) * x^(2*k-1)/(1 - x^(3*k-2)).
MATHEMATICA
a[n_] := DivisorSum[3*n - 1, # &, Mod[#, 3] == 1 &]; Array[a, 100] (* Amiram Eldar, Jun 26 2023 *)
PROG
(PARI) a(n) = sumdiv(3*n-1, d, (d%3==1)*d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 26 2023
STATUS
approved