OFFSET
1,1
COMMENTS
The arithmetic derivative of a(n) is a Giuga's number A007850 (solution of n' = n+1).
LINKS
Reinhard Zumkeller and Donovan Johnson, Table of n, a(n) for n = 1..1000 (first 100 terms from Reinhard Zumkeller)
EXAMPLE
161' = 30, 161'' = 30' = 31 ==> 161'' = 161'+1 so 161 is a term.
PROG
(PARI) /* using Michael B. Porter's code from A003415: */
A003415(n) = {local(fac); if(n<1, 0, fac=factor(n); sum(i=1, matsize(fac)[1], n*fac[i, 2]/fac[i, 1]))} /* arithmetic derivative */
/* Joerg Arndt, Apr 25 2011 */
(Haskell)
import Data.List (elemIndices)
a189710 n = a189710_list !! (n-1)
a189710_list = elemIndices 0 $
zipWith (-) (map a003415 a003415_list) (map pred a003415_list)
-- Reinhard Zumkeller, May 09 2011
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Giorgio Balzarotti, Apr 24 2011
STATUS
approved