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 178. - M. F. Hasler, Feb 24 2018
Merges into sequence A008889 after the first step.
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, B6.
Enoch Haga, Exploring Prime Numbers on Your PC, 2nd ed., 1998, pages 83-84 and Table 8, page 46. ISBN 1-885794-16-9.
LINKS
T. D. Noe, Table of n, a(n) for n = 0..178 (full sequence).
Christophe Clavier, Aliquot Sequences
Passawan Noppakaew and Prapanpong Pongsriiam, Product of Some Polynomials and Arithmetic Functions, J. Int. Seq. (2023) Vol. 26, Art. 23.9.1.
FORMULA
a(n) = A001065(a(n-1)) for n > 0, thus a(n) = A001065^n(138) for all n < 179. - M. F. Hasler, Nov 16 2013
a(n) = A008889(n-1) for all n >= 1. - M. F. Hasler, Feb 24 2018
MAPLE
f := proc(n) option remember; if n = 0 then 138; else sigma(f(n-1))-f(n-1); fi; end:
MATHEMATICA
FixedPointList[If[# > 0, DivisorSigma[1, #] - #, 0]&, 138] // Most (* Jean-François Alcover, Mar 28 2020 *)
PROG
(PARI) a(n, a=138)={for(i=1, n, a=sigma(a)-a); a} \\ M. F. Hasler, Feb 24 2018
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
EXTENSIONS
Term 179 removed from b-file by Ivan Panchenko, Nov 16 2013
Edited by M. F. Hasler, Feb 24 2018
STATUS
approved