OFFSET
1,1
COMMENTS
EXAMPLE
9' = 6, 9''= 6'= 5, 9" = 9'- 1 -> 9 is in the sequence.
PROG
(PARI) ader(n) = my(fac); if(n<1, 0, fac=factor(n); sum(i=1, matsize(fac)[1], n*fac[i, 2]/fac[i, 1])); \\ A003415
isok(k) = if (!isprime(k), my(d=ader(k)); ader(d) == d - 1); \\ Michel Marcus, Mar 13 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Giorgio Balzarotti, Apr 27 2011
STATUS
approved