This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A008891 #21 Jul 08 2025 01:23:05
%S A008891 180,366,378,582,594,846,1026,1374,1386,2358,2790,4698,6192,11540,
%T A008891 12736,12664,11096,11104,10820,11944,10466,5236,6860,9940,14252,14308,
%U A008891 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 A008891 Aliquot sequence starting at 180.
%C A008891 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 A008891 R. K. Guy, Unsolved Problems in Number Theory, B6.
%H A008891 T. D. Noe, <a href="/A008891/b008891.txt">Table of n, a(n) for n = 0..52</a>
%H A008891 Christophe CLAVIER, <a href="http://christophe.clavier.free.fr/Aliquot/site/Aliquot.html">Aliquot Sequences</a>
%H A008891 <a href="/index/Al#ALIQUOT">Index entries for sequences related to aliquot parts</a>.
%F A008891 a(n+1) = A001065(a(n)). - _R. J. Mathar_, Oct 11 2017
%p A008891 f := proc(n) option remember; if n = 0 then 180; else sigma(f(n-1))-f(n-1); fi; end:
%t A008891 FixedPointList[If[# > 0, DivisorSigma[1, #] - #, 0]&, 180] // Most (* _Jean-François Alcover_, Mar 28 2020 *)
%o A008891 (PARI) a(n,a=180)={for(i=1,n,a=sigma(a)-a);a} \\ _M. F. Hasler_, Feb 24 2018
%Y A008891 Cf. A008885 (starting at 30), ..., A008892 (starting at 276), A098007 (length of aliquot sequences).
%K A008891 nonn,fini,full
%O A008891 0,1
%A A008891 _N. J. A. Sloane_
%E A008891 Edited by _M. F. Hasler_, Feb 24 2018