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 A261532 #18 Sep 08 2022 08:46:13 %S A261532 7,589,11064985,7835767761026353,7859104819806710982081319640824417, %T A261532 15811975313589523224392147529414564125936123169432771986649715567359169 %N A261532 Hall's sequence g_n. %H A261532 James S. Hall, <a href="http://jlms.oxfordjournals.org/content/s1-28/3/285.extract">A remark on the primeness of Mersenne numbers</a>, J. London Math. Soc. 28, (1953), 285-287. %F A261532 a(n) = g(n) where g(3) = 7 and g(n+1) = 2*(g(n)-1)*(1+2^n*(g(n)-1)) + 1. %o A261532 (PARI) N=11; g=vector(N); g[3] = 7; %o A261532 for (n=3, N-1, g[n+1] = 2*(g[n]-1)*(1+2^n*(g[n]-1))+1 ); %o A261532 vector(N-3, j, g[j+2]) %o A261532 (Magma) [n le 1 select 7 else 2*(Self(n-1)-1)*(1+2^(n+1)*(Self(n-1)-1)) + 1: n in [1..6]]; // _Vincenzo Librandi_, Aug 24 2015 %Y A261532 Cf. A002812, A003010. %K A261532 nonn %O A261532 3,1 %A A261532 _Joerg Arndt_, Aug 24 2015