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 A183075 #9 Feb 18 2019 06:21:11 %S A183075 1,3,7,31,63,127,1023,8191,16383,32767,131071,524287,67108863, %T A183075 1073741823,2147483647,17179869183,274877906943,8796093022207, %U A183075 2251799813685247,2305843009213693951 %N A183075 Numbers of the form 2^k - 1 for which each prime divisor has the form 4j + 3. %C A183075 The Mersenne primes (A000668) are contained in this sequence. %C A183075 Needed factorizations are in the Cunningham Project. %H A183075 Amiram Eldar, <a href="/A183075/b183075.txt">Table of n, a(n) for n = 1..54</a> %H A183075 S. S. Wagstaff, Jr., <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>. %F A183075 a(n) = 2^A183071(n) - 1. %e A183075 63 = 2^6 - 1 = 3^2 * 7, and 3 and 7 have the form 4j + 3. %Y A183075 Cf. A000668, A136005, A183076, A183077, A183078. %Y A183075 Cf. A000043, A136003, A183071, A183072, A183073, A183074. %K A183075 nonn,hard %O A183075 1,2 %A A183075 _Stuart Clary_, Dec 23 2010