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 A073033 #12 Aug 18 2024 05:16:20 %S A073033 18656380,20522060,28630036,24289964,18656380,20522060,28630036, %T A073033 24289964,18656380,20522060,28630036,24289964,18656380,20522060, %U A073033 28630036,24289964,18656380,20522060,28630036,24289964,18656380,20522060,28630036,24289964 %N A073033 A 4-cycle of the k => sigma(k)-k process, where sigma(k) is the sum of divisors of k (A000203). %C A073033 18656380 = 2^2*5*932819, 20522060 = 2^2*5*13*17*4643, 28630036 = 2^2*19*449*839, 24289964 = 2^2*97*62603. %C A073033 The cycle was discovered by Cohen (1970). - _Amiram Eldar_, Aug 18 2024 %H A073033 Henri Cohen, <a href="https://doi.org/10.1090/S0025-5718-1970-0271004-6">On amicable and sociable numbers</a>, Math. Comp., Vol. 24, No. 110 (1970), pp. 423-429. %H A073033 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1). %o A073033 (PARI) a(n)=[24289964, 18656380, 20522060, 28630036][n%4+1] \\ _Charles R Greathouse IV_, Feb 19 2013 %Y A073033 Cf. A000203, A073032, A090615. %K A073033 nonn,easy %O A073033 1,1 %A A073033 _Miklos Kristof_, Aug 22 2002