OFFSET
1,2
FORMULA
If p is prime, a(p) = 4 + 3*p + p^2.
MATHEMATICA
a[n_]:= Sum[i*j*k/LCM[i, j, k], {i, (d = Divisors[n])}, {j, d}, {k, d}]; Array[a, 50] (* Amiram Eldar, May 10 2021 *)
PROG
(PARI) a(n) = sumdiv(n, i, sumdiv(n, j, sumdiv(n, k, i*j*k/lcm([i, j, k]))));
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Seiichi Manyama, May 10 2021
STATUS
approved