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 A112775 #20 Jul 21 2025 21:40:30 %S A112775 4,8,9,14,15,19,20,22,24,28,31,34,36,39,41,42,43,44,48,49,50,53,59,60, %T A112775 65,67,69,71,74,75,78,80,82,84,85,86,88,89,92,93,94,97,98,108,109,111, %U A112775 113,114,116,117,120,124,127,130,132,133,136,139,140,144,145,148,149 %N A112775 Numbers k such that 6k+1 is semiprime. %H A112775 Vincenzo Librandi, <a href="/A112775/b112775.txt">Table of n, a(n) for n = 1..1000</a> %F A112775 a(n) = (A112771(n) - 1)/6. %t A112775 Select[Range[200],Plus@@Last/@FactorInteger[6#+1]==2&] (* _Vincenzo Librandi_, Sep 22 2012 *) %o A112775 (Magma) IsSemiprime:=func<n | &+[k[2]: k in Factorization(n)] eq 2>; [n: n in [2..150] | IsSemiprime(6*n+1)]; // _Vincenzo Librandi_, Sep 22 2012 %Y A112775 Cf. A112771 (resulting semiprimes). %K A112775 easy,nonn %O A112775 1,1 %A A112775 _Jonathan Vos Post_ and _Ray Chandler_, Oct 15 2005