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 A097478 #31 Jun 27 2025 19:08:49 %S A097478 9,17,35,53,85,117 %N A097478 Atomic numbers of halogens in the periodic table. %C A097478 The halogens are all on the second rightmost column of the periodic table. (The rightmost column belongs to the noble gases.) - _Alonso del Arte_, Apr 26 2011 %C A097478 Halogens: 9, fluorine (F); 17;,chlorine (Cl); 35, bromine (Br); 53, iodine (I); 85, astatine (At); and 117, tennessine (Ts). - _Daniel Forgues_, Jul 13 2015, _Luca Khan_, Sep 09 2024 %D A097478 Monica Halka and Brian Nordstrom, Halogens and Noble Gases, Facts On File (2010), Part 1: The Halogens. %H A097478 Bodner Research Web, <a href="http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/group7.php">The Chemistry of the Halogens</a> %H A097478 Royal Society of Chemistry, <a href="http://www.rsc.org/periodic-table">Periodic Table</a>, 2015. %H A097478 Wikipedia, <a href="https://en.m.wikipedia.org/wiki/Halogen">Halogen</a> %F A097478 a(1) = 9; a(n) = a(n-1) + 2 * (ceiling(n/2) + 1)^2, 2 <= n <= 6. %Y A097478 Cf. A099955, alkali metals; A099956, alkaline earth metals; A101648, metalloids; A101647, nonmetals (except halogens and noble gases); A018227, noble gases; A101649, poor metals. %K A097478 nonn %O A097478 1,1 %A A097478 _Parthasarathy Nambi_, Sep 19 2004