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 A133609 #19 Mar 29 2025 17:24:53
%S A133609 183,287,319,411,413,469,515,533,579,667,685,789,813,1055,1077,1133,
%T A133609 1145,1165,1203,1253,1313,1347,1383,1385,1387,1389,1561,1685,1687,
%U A133609 1793,1795,1817,1839,1849,1919,1937,1957,1959,2045,2047,2155,2227,2315,2317
%N A133609 Numbers k such that k, k+2 and k+4 are consecutive semiprimes.
%C A133609 Terms k in A136196 such that k+2 are also in A136196.
%C A133609 All terms are odd, so it is a subsequence of A161945. - _Michel Marcus_, Oct 15 2013
%H A133609 Charles R Greathouse IV, <a href="/A133609/b133609.txt">Table of n, a(n) for n = 1..10000</a>
%e A133609 183, 185 and 187 are 59th, 60th and 61st semiprimes,
%e A133609 287, 289 and 291 are 89th, 90th and 91st semiprimes,
%e A133609 319, 321 and 323 are 101st, 102nd and 103rd semiprimes.
%t A133609 Select[Range[2317],AllTrue[{#,#+2,#+4},PrimeOmega[#]==2&]&&AllTrue[{#+1,#+3},PrimeOmega[#]!=2&]&] (* _James C. McMahon_, Mar 29 2025 *)
%o A133609 (PARI) isok(n) = (bigomega(n) == 2) && (bigomega(n+1) != 2) && (bigomega(n+2) == 2) && (bigomega(n+3) != 2) && (bigomega(n+4) == 2); \\ _Michel Marcus_, Oct 15 2013
%Y A133609 Cf. A136196.
%K A133609 nonn
%O A133609 1,1
%A A133609 _Zak Seidov_, Dec 28 2007