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A363890
Sum of divisors of 3*n-1 of form 3*k+2.
5
2, 5, 10, 11, 16, 17, 27, 23, 28, 29, 42, 40, 40, 41, 57, 47, 57, 53, 80, 59, 64, 70, 87, 71, 76, 88, 115, 83, 88, 89, 117, 100, 114, 101, 140, 107, 128, 113, 147, 136, 124, 130, 170, 131, 136, 137, 216, 154, 148, 149, 200, 160, 160, 184, 207, 167, 194, 173, 241, 179, 224, 190, 237
OFFSET
1,1
LINKS
FORMULA
a(n) = A078182(3*n-1).
G.f.: Sum_{k>0} (3*k-1) * x^k/(1 - x^(3*k-1)).
MATHEMATICA
a[n_] := DivisorSum[3*n - 1, # &, Mod[#, 3] == 2 &]; Array[a, 100] (* Amiram Eldar, Jun 26 2023 *)
PROG
(PARI) a(n) = sumdiv(3*n-1, d, (d%3==2)*d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 26 2023
STATUS
approved