OFFSET
1,1
COMMENTS
The fourth A003415-iteration of a(n) is the first to be 0.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10001 (the first 1000 terms from T. D. Noe)
FORMULA
For all n, A327969(a(n)) <= 4. - Antti Karttunen, Oct 19 2019
MATHEMATICA
dn[0] = 0; dn[1] = 0; dn[n_?Negative] := -dn[-n]; dn[n_] := Module[{f = Transpose[FactorInteger[n]]}, If[PrimeQ[n], 1, Total[n*f[[2]]/f[[1]]]]]; Select[Range[1000], dn[dn[dn[#]]] == 1&] (* T. D. Noe, Mar 07 2013 *)
PROG
(PARI)
A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jun 25 2011
EXTENSIONS
More terms from Olivier Gérard, Jul 04 2011
New primary definition added to the name by Antti Karttunen, Oct 19 2019
STATUS
approved