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 A131458 #3 Nov 11 2010 07:34:06 %S A131458 0,6,30,126,1565,8190,131070,524286,7511964,89777599,2147483646, %T A131458 20166585982,840455563322,4787976306682,5519162753736, %U A131458 2617809209727498,334169564069012755,2305843009213693950,47306781863857413639 %N A131458 Residues of 3^(2^(p(n)-1)-1) for Mersenne numbers with prime indices. %C A131458 Mp is prime iff 3^(2^(p(n)-1)-1) is congruent to (-1) Mod Mp. Thus M7 = 127 is prime because 3^63 Mod 127 = 126 (=127-1) while M11 = 2047 is composite because 3^1023 Mod 2047 <> 2046. %H A131458 Dennis Martin, <a href="/A131458/b131458.txt">Table of n, a(n) for n = 1..100</a> %F A131458 a(n) = 3^(2^(p(n)-1)-1) Mod 2^p(n)-1 %e A131458 a(5) = 3^(2^(11-1)-1) Mod 2^11-1 = 3^1023 Mod 2047 = 1565 %Y A131458 Cf. A095847, A001348, A131459, A131460, A131461, A131462, A131463. %K A131458 nonn %O A131458 1,2 %A A131458 Dennis Martin (dennis.martin(AT)dptechnology.com), Jul 13 2007, Jul 20 2007