OFFSET
1,2
LINKS
Vaclav Kotesovec, Asymptotics of Sum_{k=1..n} a(k) with a graph
FORMULA
MATHEMATICA
A018804[n_] := Sum[GCD[n, k], {k, 1, n}]; a[n_] := Sum[A018804[d] A018804[n/d], {d, Divisors[n]}]; Table[a[n], {n, 1, 55}]
f[p_, e_] := (e + 1)*p^(e - 2)*((e + 2)*(e + 3)*p^2 - 2*e*(e + 2)*p + e*(e - 1))/6; a[1] = 1; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 55] (* Amiram Eldar, Nov 25 2021 *)
PROG
(PARI)
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Ilya Gutkovskiy, Nov 25 2021
STATUS
approved