OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
G.f.: Sum_{n>=0} (3*n+2)*x^(3*n+2)/(1-x^(3*n+2)).
A078181(n) + a(n) + 3*A000203(n/3) = A000203(n), where A000203 is defined as zero for non-integer arguments. - R. J. Mathar, May 11 2016
Sum_{k=1..n} a(k) = c * n^2 + O(n*log(n)), where c = Pi^2/36 = 0.274155... (A353908). - Amiram Eldar, Nov 26 2023
MAPLE
A078182 := proc(n)
a := 0 ;
for d in numtheory[divisors](n) do
if modp(d, 3) =2 then
a :=a+d ;
end if;
end do:
a;
end proc: # R. J. Mathar, May 11 2016
MATHEMATICA
a[n_] := Plus @@ Select[Divisors[n], Mod[#, 3] == 2 &]; Array[a, 100] (* Giovanni Resta, May 11 2016 *)
PROG
(PARI) a(n) = sumdiv(n, d, d*((d%3) == 2)); \\ Michel Marcus, May 11 2016
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Nov 21 2002
STATUS
approved