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 A038581 #16 Feb 16 2025 08:32:38 %S A038581 11,20,27,47,45,90,16,180,134,76,89,115,396,184,135,245,471,405,825, %T A038581 124,1001,220,874,769,405,15,944,1671,1320,45,1309,2410,1365,876,280, %U A038581 2446,5460,1519,310,1485,680,855,795,481,6440,3640,1680,2416,155,6525,4455,585,4459 %N A038581 Absolute value of first differences of A038552, divided by 24. %H A038581 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ClassNumber.html">Class Number</a> %F A038581 a(n) = abs(A038552(n+1)-A038552(n))/24. %Y A038581 Cf. A038552. %K A038581 nonn %O A038581 1,1 %A A038581 Robert Brewer (rbrewerjr(AT)aol.com) %E A038581 Corrected and extended by _Michel Marcus_, Apr 29 2016