OFFSET
1,1
FORMULA
Sum_{d|n, gcd(d, n/d) = 1} (-1)^omega(n/d) * a(d) = prime(n).
MATHEMATICA
a[n_] := Sum[If[GCD[n/d, d] == 1, Prime[d], 0], {d, Divisors[n]}]; Table[a[n], {n, 1, 60}]
PROG
(PARI) a(n) = sumdiv(n, d, if (gcd(d, n/d) ==1, prime(d))); \\ Michel Marcus, Mar 10 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Mar 10 2020
STATUS
approved