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 A346419 #10 Feb 16 2025 08:34:02 %S A346419 2,4,1,10,16,2,6,20,4,3,30,8,8,2,340,1,5,394,48,10,10,4,16,5,22,3040, %T A346419 2,46,70,12,12,74,50,6,64,26,6964,20,1,48670,96,4,2,100,3,7,10,178,30, %U A346419 302,198,1060,8,39,126,16,16,130,97684,8,25,502,6960,2,2136,86,4,340,9,106,160,1,18,164,5,9,20810 %N A346419 a(n) is twice the coefficient of 1 in the fundamental unit of Q(sqrt(A000037(n))) where A000037 lists the nonsquare numbers (Version 2). %H A346419 S. R. Finch, <a href="https://web.archive.org/web/20160511035657/http://www.people.fas.harvard.edu/~sfinch/csolve/clss.pdf">Class number theory</a> %H A346419 Steven R. Finch, <a href="/A000924/a000924.pdf">Class number theory</a> [Cached copy, with permission of the author] %H A346419 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FundamentalUnit.html">Fundamental Unit</a>. %t A346419 nonSquares = Select[Range[72], !IntegerQ[Sqrt[#]]& ]; 2*NumberFieldFundamentalUnits[Sqrt[#]][[1, 2, 1]] & /@ nonSquares (* _Jean-François Alcover_, Nov 09 2012 *) %o A346419 (PARI) for(n=1,30,if(!issquare(n),print1(abs(2*polcoeff(lift(bnfinit(x^2-n).fu[1]),0)),","))) /* _Ralf Stephan_, Sep 18 2013; updated by _Michel Marcus_, Jun 25 2020 */ %Y A346419 Cf. A000037, A346420, A048941, A048942. %K A346419 nonn %O A346419 1,1 %A A346419 _Sean A. Irvine_