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 A008887 #19 Jul 08 2025 01:22:46 %S A008887 60,108,172,136,134,70,74,40,50,43,1,0 %N A008887 Aliquot sequence starting at 60. %C A008887 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 11. - _M. F. Hasler_, Feb 24 2018 %D A008887 R. K. Guy, Unsolved Problems in Number Theory, B6. %H A008887 Christophe CLAVIER, <a href="http://christophe.clavier.free.fr/Aliquot/site/Aliquot.html">Aliquot Sequences</a> %H A008887 <a href="/index/Al#ALIQUOT">Index entries for sequences related to aliquot parts</a>. %F A008887 a(n+1) = A001065(a(n)). - _R. J. Mathar_, Oct 11 2017 %p A008887 f := proc(n) option remember; if n = 0 then 60; else sigma(f(n-1))-f(n-1); fi; end: %t A008887 NestList[If[#==0,0,DivisorSigma[1,#]-#]&,60,80] (* _Harvey P. Dale_, Nov 29 2013 *) %o A008887 (PARI) a(n,a=60)=for(i=1,n,a=sigma(a)-a);a \\ Will raise an error for n > 11, in agreement with the definition. - _M. F. Hasler_, Feb 24 2018 %Y A008887 Cf. A008885 (starting at 30), ..., A008892 (starting at 276), A098007 (length of aliquot sequences). %K A008887 nonn,fini,full %O A008887 0,1 %A A008887 _N. J. A. Sloane_ %E A008887 Edited by _M. F. Hasler_, Feb 24 2018