OFFSET
1,3
COMMENTS
A divisor, d, of n is isolated if neither (d-1) nor (d+1) divides n.
The convention for 1 is that it is an isolated divisor iff n is not even. - Olivier Gérard, Sep 22 2007
LINKS
Jens Kruse Andersen, Table of n, a(n) for n = 1..10000
EXAMPLE
The positive divisors of 56 are: 1,2,4,7,8,14,28,56. Of these, 1 and 2 are adjacent and 7 and 8 are adjacent. The isolated divisors are therefore 4,14, 28,56. So a(56) = 4 +14 +28 +56 = 102.
MATHEMATICA
Table[Plus@@Select[Divisors[n], (#==1||Mod[n, #-1]>0)&&Mod[n, #+1]>0&], {n, 1, 200}] (* Olivier Gérard, Sep 22 2007 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Sep 03 2007
EXTENSIONS
More terms from Olivier Gérard, Sep 22 2007
STATUS
approved