OFFSET
1,2
COMMENTS
Sum of prime factors of n (counted with multiplicity) with odd indices minus the sum of prime factors of n (counted with multiplicity) with even indices.
LINKS
EXAMPLE
a(252) = a(2^2 * 3^2 * 7) = a(prime(1)^2 * prime(2)^2 * prime(4)) = 2 + 2 - 3 - 3 - 7 = -9.
MATHEMATICA
a[n_] := Plus @@ ((-1)^(PrimePi[#[[1]]] + 1) #[[1]] #[[2]] & /@ FactorInteger[n]); a[1] = 0; Table[a[n], {n, 1, 69}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Feb 12 2020
STATUS
approved