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 A008885 #33 Jul 08 2025 01:22:35 %S A008885 30,42,54,66,78,90,144,259,45,33,15,9,4,3,1,0 %N A008885 Aliquot sequence starting at 30. %C A008885 The sum-of-divisor function A000203 and thus aliquot parts A001065 are defined only for positive integers, so the trajectory ends when 0 is reached, here at index 15. - _M. F. Hasler_, Feb 24 2018 %D A008885 Richard K. Guy, Unsolved Problems in Number Theory, B6. %H A008885 Christophe CLAVIER, <a href="http://christophe.clavier.free.fr/Aliquot/site/Aliquot.html">Aliquot Sequences</a> %H A008885 R. J. Mathar, <a href="/A115350/a115350.pdf">Illustration of Aliquot Sequence Mergers</a> (2014) Fig 1 (prime family 3) %H A008885 <a href="/index/Al#ALIQUOT">Index entries for sequences related to aliquot parts</a>. %F A008885 a(n+1) = A001065(a(n)). - _R. J. Mathar_, Oct 11 2017 %e A008885 a(0) = 30. %e A008885 30 has eight divisors, 1, 2, 3, 5, 6, 10, 15, 30, which add up to 72, and 72 - 30 = 42, so a(1) = 42. %p A008885 f := proc(n) option remember; if n = 0 then 30; else sigma(f(n-1))-f(n-1); fi; end: %t A008885 NestList[If[# > 0, DivisorSigma[1, #] - #, 0] &, 30, 80] (* _Harvey P. Dale_, Jun 12 2012 *) %o A008885 (PARI) a(n, a=30)=for(i=1, n, a=sigma(a)-a); a \\ _M. F. Hasler_, Feb 24 2018 %Y A008885 Cf. A008886, A008887, A008888, A008889, A008890, A008891, A008892. %K A008885 nonn,fini,full %O A008885 0,1 %A A008885 _N. J. A. Sloane_ %E A008885 Edited by _M. F. Hasler_, Feb 24 2018