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 A125055 #11 May 11 2014 22:35:14 %S A125055 1,15,285,8475,378105,23823015,2018820885,221605991475,30596648805105, %T A125055 5189967817758015,1061021392126671885,257296819626005894475, %U A125055 73023341368629447792105,23978466652359211809453015 %N A125055 Diagonal of symmetric triangle A125053 located immediately below the central terms (A125054). %C A125055 Triangle A125053 is a variant of triangle A008301 (enumeration of binary trees) such that the leftmost column gives the secant numbers (A000364). %F A125055 a(n) = A125054(n+1) - 2*A125054(n). - _Philippe Deléham_, Jul 22 2007 %Y A125055 Cf. A125053, A125054. %K A125055 nonn %O A125055 0,2 %A A125055 _Paul D. Hanna_, Nov 21 2006