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 A190299 #19 Feb 16 2025 08:33:14
%S A190299 21,33,57,65,69,77,85,93,129,133,141,145,161,177,185,201,205,209,213,
%T A190299 217,221,237,249,253,265,301,305,309,321,329,341,365,377,381,393,413,
%U A190299 417,437,445,453,469,473,481,485,489,493,497,501,505,517,533,537,545
%N A190299 Squarefree semiprimes of the form 4k+1.
%C A190299 There are 961 squarefree semiprimes of the form 4k+1 below 10000.
%H A190299 T. D. Noe, <a href="/A190299/b190299.txt">Table of n, a(n) for n = 1..1000</a>
%H A190299 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Semiprime.html">Semiprime</a>
%H A190299 Wikipedia, <a href="http://en.wikipedia.org/wiki/Semiprime">Semiprime</a>
%t A190299 Select[Range[1,600,4],Last/@FactorInteger[#]=={1,1}&]
%Y A190299 Cf. A001358, A006881, A080774. Union of A131574 and A016105.
%K A190299 nonn
%O A190299 1,1
%A A190299 _Vladimir Joseph Stephan Orlovsky_, May 07 2011
%E A190299 Edited by _Ray Chandler_, Dec 16 2011