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 A203777 #41 Mar 04 2024 01:14:55
%S A203777 220,284,220,284,220,284,220,284,220,284,220,284,220,284,220,284,220,
%T A203777 284,220,284,220,284,220,284,220,284,220,284,220,284,220,284,220,284,
%U A203777 220,284,220,284,220,284,220,284,220,284,220,284,220,284,220,284,220,284
%N A203777 Aliquot sequence starting at 220.
%C A203777 A period 2 sequence.
%C A203777 The sum of the proper divisors of 220 is 284 and the sum of the proper divisors of 284 is 220.
%C A203777 Sierpiński's book has typos for n = 1 and 3 (280 instead of 284).
%C A203777 Also continued fraction expansion of (7810+sqrt(61000005))/71. - _Bruno Berselli_, Jan 18 2012
%D A203777 Wacław Sierpiński, Czym sie zajmuje teoria liczb. Warsaw: PW "Wiedza Powszechna", 1957, p. 138.
%H A203777 J. Perrott, <a href="https://doi.org/10.24033/bsmf.394">Sur une proposition empirique énoncée au Bulletin</a>, Bulletin de la S. M. F., tome 17 (1889), pp. 155-156.
%H A203777 Wikipedia, <a href="http://en.wikipedia.org/wiki/Aliquot_sequence">Aliquot sequence</a>.
%H A203777 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,1).
%F A203777 a(2*n) = 220, a(2*n+1) = 284.
%F A203777 a(n+1) = A001065(a(n)). - _R. J. Mathar_, Oct 11 2017
%e A203777 a(0) = 220, a(1) = sigma(220) - 220 = 284.
%t A203777 RecurrenceTable[{a[n] == DivisorSigma[1, a[n - 1]] - a[n - 1], a[0] == 220}, a, {n, 51}]
%Y A203777 Cf. A001065, A063990.
%K A203777 nonn,easy
%O A203777 0,1
%A A203777 _Arkadiusz Wesolowski_, Jan 05 2012