OFFSET
0,1
COMMENTS
The sum-of-divisor function A000203 and aliquot parts A001065 are defined only for positive integers, so the trajectory ends when 0 is reached, here at index 175. - M. F. Hasler, Feb 24 2018
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, B6.
LINKS
T. D. Noe, Table of n, a(n) for n = 0..175 (a(176) removed by Georg Fischer, Apr 28 2019)
Christophe Clavier, Aliquot Sequences
FORMULA
a(n+1) = A001065(a(n)). - R. J. Mathar, Oct 11 2017
MAPLE
f := proc(n) option remember; if n = 0 then 168; else sigma(f(n-1))-f(n-1); fi; end:
MATHEMATICA
NestList[DivisorSigma[1, #] - # &, 168, 175] (* Alonso del Arte, Feb 24 2018 *)
PROG
(PARI) a(n, a=168)={for(i=1, n, a=sigma(a)-a); a} \\ M. F. Hasler, Feb 24 2018
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
EXTENSIONS
Edited by M. F. Hasler, Feb 24 2018
STATUS
approved