OFFSET
1,2
FORMULA
a(n) = Sum_{i|n, j|n, k|n} n/gcd(i,j,k).
If p is prime, a(p) = 1 + 7*p.
MATHEMATICA
a[n_]:= Sum[n/GCD[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, lcm([i, j, k]))));
(PARI) a(n) = sumdiv(n, i, sumdiv(n, j, sumdiv(n, k, n/gcd([i, j, k]))));
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
Seiichi Manyama, May 10 2021
STATUS
approved