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A372709
a(n) = Sum_{k=1..n} tau(n*k), where tau(n) = number of divisors of n, cf. A000005.
2
1, 5, 9, 18, 19, 41, 31, 56, 59, 83, 57, 136, 73, 127, 151, 170, 103, 233, 119, 270, 239, 233, 151, 406, 241, 285, 311, 424, 205, 579, 225, 464, 425, 399, 473, 758, 283, 459, 517, 812, 319, 891, 339, 742, 853, 587, 375, 1138, 571, 893, 731, 920, 437, 1157, 847, 1250
OFFSET
1,2
FORMULA
Conjecture: a(n) ~ A372674(n) / 2. - Vaclav Kotesovec, May 13 2024
MATHEMATICA
Table[Sum[DivisorSigma[0, k*n], {k, 1, n}], {n, 1, 50}] (* Vaclav Kotesovec, May 13 2024 *)
PROG
(PARI) a(n) = sum(k=1, n, numdiv(n*k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, May 11 2024
STATUS
approved