Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #19 Mar 28 2020 10:13:16
%S 180,366,378,582,594,846,1026,1374,1386,2358,2790,4698,6192,11540,
%T 12736,12664,11096,11104,10820,11944,10466,5236,6860,9940,14252,14308,
%U 15218,10894,6746,3376,3196,2852,2524,1900,2440,3140,3496,3704,3256,3584,4600,6560,9316,8072,7078,3542,3370,2714,1606,1058,601,1,0
%N Aliquot sequence starting at 180.
%C 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 52. - _M. F. Hasler_, Feb 24 2018
%D R. K. Guy, Unsolved Problems in Number Theory, B6.
%H T. D. Noe, <a href="/A008891/b008891.txt">Table of n, a(n) for n = 0..52</a>
%H Christophe CLAVIER, <a href="http://christophe.clavier.free.fr/Aliquot/site/Aliquot.html">Aliquot Sequences</a>
%H <a href="/index/Al#ALIQUOT">Index entries for sequences related to aliquot parts</a>.
%F a(n+1) = A001065(a(n)). - _R. J. Mathar_, Oct 11 2017
%p f := proc(n) option remember; if n = 0 then 180; else sigma(f(n-1))-f(n-1); fi; end:
%t FixedPointList[If[# > 0, DivisorSigma[1, #] - #, 0]&, 180] // Most (* _Jean-François Alcover_, Mar 28 2020 *)
%o (PARI) a(n,a=180)={for(i=1,n,a=sigma(a)-a);a} \\ _M. F. Hasler_, Feb 24 2018
%Y Cf. A008885 (starting at 30), ..., A008892 (starting at 276), A098007 (length of aliquot sequences).
%K nonn,fini,full
%O 0,1
%A _N. J. A. Sloane_.
%E Edited by _M. F. Hasler_, Feb 24 2018