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 A069977 #25 Feb 06 2023 17:59:30
%S A069977 1,3,5,11,13,15,17,19,21,29,31,33,35,37,39,41,51,53,55,57,59,65,67,69,
%T A069977 71,77,83,85,87,89,91,93,95,101,103,105,107,109,111,113,127,129,131,
%U A069977 137,139,141,143,149,155,157,159,161,163,165,177,179,181,183,185,191,193
%N A069977 Numbers k such that k and k+2 are squarefree.
%C A069977 The asymptotic density of this sequence is Product_{p prime} (1 - 2/p^2) = 0.322634... (A065474) (Mirsky, 1949). - _Amiram Eldar_, Dec 29 2020
%H A069977 Amiram Eldar, <a href="/A069977/b069977.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harvey P. Dale)
%H A069977 Bin Chen, <a href="https://arxiv.org/abs/2301.05044">On almost-prime $k$-tuples</a>, arXiv preprint (2023). arXiv:2301.05044 [math.NT], 2023.
%H A069977 Leon Mirsky, <a href="https://doi.org/10.1090/S0002-9904-1949-09313-8">On the frequency of pairs of square-free numbers with a given difference</a>, Bull. Amer. Math. Soc., Vo. 55, No. 10 (1949), pp. 936-939.
%t A069977 f[n_] := Union[ Transpose[ FactorInteger[n]] [[ -1]]] [[ -1]]; Select[ Range[200], f[ # ] < 2 && f[ # + 2] < 2 & ]
%t A069977 SequencePosition[Table[If[SquareFreeQ[n],1,0],{n,200}],{1,_,1}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 06 2017 *)
%o A069977 (PARI) is(n)=n%2 && issquarefree(n) && issquarefree(n+2) \\ _Charles R Greathouse IV_, May 15 2016
%Y A069977 Cf. A007674, A065474.
%K A069977 nonn
%O A069977 1,2
%A A069977 Sharon Sela (sharonsela(AT)hotmail.com), May 01 2002
%E A069977 Edited and extended by _Robert G. Wilson v_, May 04 2002
%E A069977 1 prepended by _Vladimir Joseph Stephan Orlovsky_, Mar 30 2011