OFFSET
1,6
EXAMPLE
The positive divisors of 20 are 1,2,4,5,10,20. Of these, 1 and 2 are adjacent and 4 and 5 are adjacent. So the isolated divisors of 20 are 10 and 20. Therefore a(21) = a(10) + a(20) = 5 + 26 = 31.
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Sep 16 2007
EXTENSIONS
Extended by Ray Chandler, Jun 25 2008
STATUS
approved