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 A077678 #26 Mar 05 2021 03:30:23 %S A077678 2,21,22,23,26,29,201,202,203,205,206,209,210,211,213,214,215,217,218, %T A077678 219,221,222,223,226,227,229,230,231,233,235,237,238,239,241,246,247, %U A077678 249,251,253,254,255,257,258,259,262,263,265,266,267,269,271,273,274 %N A077678 Squarefree numbers beginning with 2. %C A077678 Intersection of A005117 and A217394. - _Michel Marcus_, Sep 14 2013 %C A077678 Lower density is 3/(10*Pi^2), upper density is 20/(9*Pi^2). - _Charles R Greathouse IV_, Nov 05 2017 %H A077678 Amiram Eldar, <a href="/A077678/b077678.txt">Table of n, a(n) for n = 1..10000</a> %t A077678 s2Q[n_]:=First[IntegerDigits[n]]==2 && 1==Max@@Last/@FactorInteger[n]; Select[Range[274],s2Q[#] &] (* _Jayanta Basu_, May 22 2013 *) %o A077678 (PARI) is(n)=n>1 && digits(n)[1]==2 && issquarefree(n) \\ _Charles R Greathouse IV_, Nov 05 2017 %Y A077678 Cf. A077677, A077679, A077680, A077681, A077682, A077683, A077684, A077685. %K A077678 base,easy,nonn %O A077678 1,1 %A A077678 _Amarnath Murthy_, Nov 16 2002 %E A077678 More terms from _Sascha Kurz_, Jan 28 2003