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 A368560 #18 Jan 20 2024 09:09:17
%S A368560 78557,34985939,2191531,8482363,7696009,31177213,19436611,790841,
%T A368560 34629797,17710319,13085029,28482703,10391933,29829251,78557,34985939,
%U A368560 2191531,8482363,7696009,31177213,19436611,790841,34629797,17710319,13085029,28482703,10391933,29829251
%N A368560 a(1) = 78557 (the first Sierpinski number); thereafter a(n+1) = Od(3*5*7*13*19*37*73 - a(n)), where Od(m) is the odd part of m.
%C A368560 Generally, if k is a Sierpinski number (or is a Riesel number) and P(k) > k is the product of all elements from the covering set for k*2^n + 1 (or for k*2^n - 1), then Od(P(k) - k) is a Riesel number (or is a Sierpinski number) with the same covering set, where Od(m) is the odd part of m.
%C A368560 Thus a(2n-1) is a Sierpinski number and a(2n) is a Riesel number.
%C A368560 This sequence is purely periodic with period P = 14.
%H A368560 <a href="/index/Rec#order_14">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,0,0,0,0,0,1).
%F A368560 a(n + 14) = a(n).
%e A368560 a(1) = 78557 is a Sierpinski number and a(2) = (3*5*7*13*19*37*73 - 78557)/2 = 34985939 is a Riesel number with the same covering set {3, 5, 7, 13, 19, 37, 73}.
%t A368560 od[n_] := n/2^IntegerExponent[n, 2]; a[1] = 78557; a[n_] := a[n] = od[70050435 - a[n-1]]; Array[a, 42] (* _Amiram Eldar_, Dec 30 2023 *)
%Y A368560 Cf. A000265, A076336, A101036.
%K A368560 nonn,easy
%O A368560 1,1
%A A368560 _Thomas Ordowski_, Dec 30 2023