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 A121495 #7 Feb 22 2021 03:15:25 %S A121495 14,21,33,34,38,57,65,69,77,85,86,93,94,105,110,114,118,122,129,133, %T A121495 141,142,145,154,158,165,177,182,185,186,194,201,202,205,209,213,214, %U A121495 217,218,221,230,237,246,253,254,258,265,266,273,285,286,290,298,301,302 %N A121495 Numbers k such that k and k+1 are composite and squarefree. %C A121495 Numbers that are in A068780 and in A007674. %H A121495 Amiram Eldar, <a href="/A121495/b121495.txt">Table of n, a(n) for n = 1..10000</a> %e A121495 21 = 3*7 and 22 = 2*11 are squarefree, so 21 is in the sequence. %t A121495 q[n_] := CompositeQ[n] && SquareFreeQ[n]; Select[Range[300], q[#] && q[# + 1] &] (* _Amiram Eldar_, Feb 22 2021 *) %o A121495 (PARI) for(n=1,310,if(!isprime(n)&&!isprime(n+1)&&issquarefree(n)&&issquarefree(n+1),print1(n,","))) %Y A121495 Cf. A002808, A005117, A007674, A068780. %K A121495 easy,nonn %O A121495 1,1 %A A121495 _Klaus Brockhaus_, Aug 03 2006