OFFSET
1,3
EXAMPLE
a(12) = 10; a(12) = Sum_{p|12, p prime} (p-1) * tau(12/p) = (2-1)*tau(12/2) + (3-1)*tau(12/3) = tau(6) + 2*tau(4) = 4 + 2*3 = 10.
PROG
(PARI) a(n) = my(f=factor(n)); sum(k=1, #f~, (f[k, 1]-1)*numdiv(n/f[k, 1])); \\ Michel Marcus, Feb 18 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Feb 17 2022
STATUS
approved