OFFSET
1,4
FORMULA
a(n) = Sum_{d|n} d * ((1+d') mod 2).
MATHEMATICA
d[1] = 0; d[n_] := n * Plus @@ ((Last[#]/First[#]) & /@ FactorInteger[n]); a[n_] := DivisorSum[n, # &, EvenQ[d[#]] &]; Array[a, 100] (* Amiram Eldar, May 12 2022 *)
PROG
(PARI) ad(n) = vecsum([n/f[1]*f[2]|f<-factor(n+!n)~]); \\ A003415
a(n) = sumdiv(n, d, if (!(ad(d) % 2), d)); \\ Michel Marcus, May 12 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, May 12 2022
STATUS
approved