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 A066681 #18 Feb 04 2021 11:23:54 %S A066681 8,12,18,27,30,45,50,63,70,75,80,98,105,112,125,128,147,154,165,168, %T A066681 175,176,182,192,195,208,220,231,242,245,260,264,273,275,286,312,325, %U A066681 338,340,343,357,363,374,380,385,396,399,408 %N A066681 Badly sieved numbers (A066680) which are not primes. %H A066681 Reinhard Zumkeller, <a href="/A066681/b066681.txt">Table of n, a(n) for n = 1..10000</a> %H A066681 <a href="/index/Si#sieve">Index entries for sequences generated by sieves</a> %F A066681 A099104(a(n))*A005171(a(n)) = 1. [_Reinhard Zumkeller_, Nov 12 2009] %e A066681 8 is the first nonprime in A066680, as multiples of 2 are marked only up to 4 = 2^2 and all other multiples of unmarked numbers < 8 do not hit 8. %o A066681 (Haskell) %o A066681 a066681 n = a066681_list !! (n-1) %o A066681 a066681_list = filter ((== 0) . a010051) a066680_list %o A066681 -- _Reinhard Zumkeller_, Feb 17 2012 %Y A066681 Cf. A010051. %K A066681 nonn %O A066681 1,1 %A A066681 _Reinhard Zumkeller_, Dec 31 2001