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 A006243 M5412 #35 Jul 08 2025 16:44:11
%S A006243 198,7761798,467613464999866416198,
%T A006243 102249460387306384473056172738577521087843948916391508591105798
%N A006243 Extracting a square root.
%D A006243 Jeffrey Shallit, personal communication.
%D A006243 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006243 Vincenzo Librandi, <a href="/A006243/b006243.txt">Table of n, a(n) for n = 1..6</a>
%H A006243 E. B. Escott, <a href="http://www.jstor.org/stable/2301484">Rapid method for extracting a square root</a>, Amer. Math. Monthly, 44 (1937), 644-646.
%F A006243 a(1) = 198, a(n) = a(n-1)^3 - 3*a(n-1). - _Sean A. Irvine_, Feb 08 2017
%F A006243 a(n) = (99 + 70*sqrt(2))^(3^(n-1)) + (99 - 70*sqrt(2))^(3^(n-1)). - _Bruno Berselli_, Feb 10 2017
%t A006243 RecurrenceTable[{a[1]==198, a[n]==a[n-1]^3 - 3 a[n-1]}, a, {n, 8}] (* _Vincenzo Librandi_, Feb 09 2017 *)
%o A006243 (Magma) [n eq 1 select 198 else Self(n-1)^3-3*Self(n-1): n in [1..5]]; // _Vincenzo Librandi_, Feb 09 2017
%Y A006243 Cf. A006242, A112845 (differs only for the initial 6).
%K A006243 nonn
%O A006243 1,1
%A A006243 _N. J. A. Sloane_
%E A006243 Offset changed by _Sean A. Irvine_, Feb 08 2017