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 A131461 #3 Nov 11 2010 07:34:06 %S A131461 0,1,1,1,1013,1,1,1,5884965,65165529,1,103888408793,474639880182, %T A131461 4112907695371,72685811469476,5155089749987738,440411515280180314,1, %U A131461 95591506202441271281,69291880649932219827 %N A131461 Residues of 3^(2^p(n)-2) for Mersenne numbers with prime indices. %C A131461 M_p is prime iff 3^(M_p-1) is congruent to 1 mod M_p. Thus M_7 = 127 is prime because 3^126 mod 127 = 1 while M_11 = 2047 is composite because 3^2046 mod 2047 <> 1. %H A131461 Dennis Martin, <a href="/A131461/b131461.txt">Table of n, a(n) for n = 1..100</a> %F A131461 a(n) = 3^(2^p(n)-2) mod 2^p(n)-1 %e A131461 a(5) = 3^(2^11-2) mod 2^11-1 = 3^2046 mod 2047 = 1013 %Y A131461 Cf. A095847, A001348, A131458, A131459, A131460, A131462, A131463. %K A131461 nonn %O A131461 1,5 %A A131461 Dennis Martin (dennis.martin(AT)dptechnology.com), Jul 20 2007