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 A183076 #10 Feb 18 2019 06:46:17 %S A183076 63,1023,16383,32767,67108863,1073741823,17179869183,274877906943, %T A183076 8796093022207,2251799813685247,4611686018427387903, %U A183076 36893488147419103231 %N A183076 Composite numbers of the form 2^k - 1 for which each prime divisor has the form 4j + 3. %C A183076 Needed factorizations are in the Cunningham Project. %H A183076 Amiram Eldar, <a href="/A183076/b183076.txt">Table of n, a(n) for n = 1..39</a> %H A183076 S. S. Wagstaff, Jr., <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>. %F A183076 a(n) = 2^A183072(n) - 1. %e A183076 63 = 2^6 - 1 = 3^2 * 7, and 3 and 7 have the form 4j + 3. %Y A183076 Cf. A000668, A136005, A183075, A183077, A183078. %Y A183076 Cf. A000043, A136003, A183071, A183072, A183073, A183074. %K A183076 nonn,hard %O A183076 1,1 %A A183076 _Stuart Clary_, Dec 23 2010